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SUMMARY Energy is required for growth as well as for multiple cellular processes. During evolution, plants developed regulatory mechanisms to adapt energy consumption to metabolic reserves and cellular needs. Reduced growth is often observed under stress, leading to a growth‐stress trade‐off that governs plant performance under different conditions. In this work, we report that plants with reduced levels of the mitochondrial respiratory chain component cytochrome c (CYTc), required for electron transport coupled to oxidative phosphorylation and ATP production, show impaired growth and increased global expression of stress‐responsive genes, similar to those observed after inhibiting the respiratory chain or the mitochondrial ATP synthase. CYTc‐deficient plants also show activation of the SnRK1 pathway, which regulates growth, metabolism, and stress responses under carbon starvation conditions, even though their carbohydrate levels are not significantly different from wild‐type. Notably, loss‐of‐function of the gene encoding the SnRK1α1 subunit restores the growth of CYTc‐deficient plants, as well as autophagy, free amino acid and TOR pathway activity levels, which are affected in these plants. Moreover, increasing CYTc levels decreases SnRK1 pathway activation, reflected in reduced SnRK1α1 phosphorylation, with no changes in total SnRK1α1 protein levels. Under stress imposed by mannitol, the growth of CYTc‐deficient plants is relatively less affected than that of wild‐type plants, which is also related to the activation of the SnRK1 pathway. Our results indicate that SnRK1 function is affected by CYTc levels, thus providing a molecular link between mitochondrial function and plant growth under normal and stress conditions. [ABSTRACT FROM AUTHOR]

Main conclusion: This study provides evidence about the relationship between Target of Rapamycin (TOR) kinase and the signal molecule nitric oxide (NO) in plants. We showed that sucrose (SUC)-mediated TOR activation of root apical meristem (RAM) requires NO and that NO, in turn, participates in the regulation of TOR signaling. Nitric oxide (NO) constitutes a signal molecule that regulates important target proteins related to growth and development and also contributes to metabolic reprogramming that occurs under adverse conditions. Taking into account the important role of NO and its relationship with Target of Rapamycin (TOR) signaling in animals, we wondered about the putative link between both pathways in plants. With this aim, we studied a TOR-dependent process which is the reactivation of the root apical meristem (RAM) in Arabidopsis thaliana. We used pharmacological and genetic tools to evaluate the relationship between NO and TOR on the sugar induction of RAM, using SNP as NO donor, cPTIO as NO scavenger and the nitrate reductase (NR) mutant nia2. The results showed that sucrose (SUC)-mediated TOR activation of the RAM requires NO and that NO, in turn, participates in the regulation of TOR signaling. Interestingly, TOR activation induced by sugar increased the NO levels. We also observed that NO could mediate the repression of SnRK1 activity by SUC. By computational prediction we found putative S-nitrosylation sites in the TOR complex proteins and the catalytic subunit of SnRK1, SnRK1.1. The present work demonstrates for the first time a link between NO and TOR revealing the complex interplay between the two pathways in plants. [ABSTRACT FROM AUTHOR]

Abstract The SnRK1, hexokinase, and TORC1 (TOR, LST8, RAPTOR) are three pivotal kinases at the core of sugar level sensing, significantly impacting plant metabolism and development. We retrieved and analyzed protein sequences of these three kinase pathways from seven sugarcane transcriptome and genome datasets, identifying protein domains, phylogenetic relationships, sequence ancestry, and in silico expression levels. Additionally, we predicted HXK subcellular localization and assessed its enzymatic activity in sugarcane leaves and culms along development in the field. We retrieved 11 TOR, 23 RAPTOR, 55 LST8, 95 SnRK1α, 98 HXK, and 14 HXK-like putative full-length sequences containing all the conserved domains. Most of these transcripts seem to share a common origin with the three ancestral species of sugarcane: Saccharum officinarum, Saccharum spontaneum, and Saccharum barberi. We accessed the expression profile of sequences from one sugarcane transcriptome. We found the highest enzymatic activity of HXK in culms in the first month, which, at this stage, provides carbon (sucrose) and nitrogen (amino acids) for initial plant development. Our approach places novel sugar sensing sequences that work as a guideline for further research into the underlying signaling mechanisms and biotechnology applications in sugarcane.

Sugar signaling governed by SNF1-RELATED PROTEIN KINASE 1 (SnRK1), TARGET OF RAPAMYCIN (TOR), and trehalose 6-phosphate (T6P) balances energy for root growth. T6P emerges as a central regulator linking auxin, SnRK1, and TOR in root development. A mechanism is emerging in which SnRK1 inhibits TOR through phosphorylation, while T6P can obstruct SnRK1 activity through interaction with TPS class II proteins, thereby controlling the energy that can be used for root development. Sugars derived from photosynthesis, specifically sucrose, are the primary source of plant energy. Sucrose is produced in leaves and transported to the roots through the phloem, serving as a vital energy source. Environmental conditions can result in higher or lower photosynthesis, promoting anabolism or catabolism, respectively, thereby influencing the sucrose budget available for roots. Plants can adjust their root system to optimize the search for soil resources and to ensure the plant's adaptability to diverse environmental conditions. Recently, emerging research indicates that SNF1-RELATED PROTEIN KINASE 1 (SnRK1), trehalose 6-phosphate (T6P), and TARGET OF RAPAMYCIN (TOR) collectively serve as fundamental regulators of root development, together forming a signaling module to interpret the nutritional status of the plant and translate this to growth adjustments in the below ground parts. [ABSTRACT FROM AUTHOR]

Sucrose non-fermenting (SNF) related protein kinase 1 (SnRK1) is a master regulator of energy deprivation signaling, has also been implicated in abiotic and biotic stress regulation. SnRK1 promotes stress tolerance through metabolic and transcriptional changes and plays important roles in innate immunity against various pathogens. However, whether it plays a role against insect herbivory is not understood. To test this, using the wild type (with SnRK1) and snrk1 mutant lines in rice, we examined the potential role of SnRK1 in rice against the ruinous pest, Fall armyworm (FAW), Spodoptera frugiperda. We also investigated the response of FAW towards these lines at different time intervals after exogenous application of plant hormone, Jasmonic acid (JA), and a JA blocker (Ibuprofen). Additional experiments by feeding FAW with leaf infused diet, fresh leaves, and a short-term exposure of FAW to the lines were also carried out. FAW mass gain, growth and development, and host ecophysiological traits were observed. In addition, we also quantified the major surface defenses- trichomes, and wax before and after herbivory. Our results show that FAW response did not vary between mutants and wild type rice. Meanwhile, we found plant hormonal application influenced the ecophysiological traits regardless of mutants and wild type rice. Collectively, we show that while defense against FAW in rice is JA mediated, SnRK1 has a limited role as observed through manipulative experiments with the wild type and snrk1 mutant rice lines.

Summary: Regulation of grain size is a crucial strategy for improving the crop yield and is also a fundamental aspect of developmental biology. However, the underlying molecular mechanisms governing grain development in wheat remain largely unknown. In this study, we identified a wheat atypical basic helix–loop–helix (bHLH) transcription factor, TabHLH489, which is tightly associated with grain length through genome‐wide association study and map‐based cloning. Knockout of TabHLH489 and its homologous genes resulted in increased grain length and weight, whereas the overexpression led to decreased grain length and weight. TaSnRK1α1, the α‐catalytic subunit of plant energy sensor SnRK1, interacted with and phosphorylated TabHLH489 to induce its degradation, thereby promoting wheat grain development. Sugar treatment induced TaSnRK1α1 protein accumulation while reducing TabHLH489 protein levels. Moreover, brassinosteroid (BR) promotes grain development by decreasing TabHLH489 expression through the transcription factor BRASSINAZOLE RESISTANT1 (BZR1). Importantly, natural variations in the promoter region of TabHLH489 affect the TaBZR1 binding ability, thereby influencing TabHLH489 expression. Taken together, our findings reveal that the TaSnRK1α1‐TabHLH489 regulatory module integrates BR and sugar signalling to regulate grain length, presenting potential targets for enhancing grain size in wheat. [ABSTRACT FROM AUTHOR]

Sucrose non-fermenting-1-related protein kinase 1 (SnRK1) and AMP-activated protein kinase (AMPK) are highly conserved. Compound 991 is an AMPK activator in mammals. However, whether 991 also activates SnRK1 remains unknown. The addition of 991 significantly increased SnRK1 activity in desalted extracts from germinating rice seeds in vitro. To determine whether 991 has biological activity, rice seeds were treated with different concentrations of 991. Germination was promoted at low concentrations but inhibited at high concentrations. The effects of 991 on germination were similar to those of OsSnRK1a overexpression. To explore whether 991 affects germination by specifically affecting SnRK1, germination of an snrk1a mutant and the wild type under 1 μM 991 treatment was compared. The snrk1a mutant was insensitive to 991. Phosphoproteomic analysis showed that the differential phosphopeptides induced by 991 and OsSnRK1a overexpression largely overlapped. Furthermore, SnRK1 might regulate rice germination in a dosage-dependent manner by regulating the phosphorylation of three phosphosites, namely S285-PIP2;4, S1013-SOS1, and S110-ABI5. These results indicate that 991 is a specific SnRK1 activator in rice. The promotion and inhibition of germination by 991 also occurred in wheat seeds. Thus, 991 is useful for exploring SnRK1 function and the chemical regulation of growth and development in crops. [ABSTRACT FROM AUTHOR]

During maize endosperm filling, sucrose not only serves as a source of carbon skeletons for storage-reserve synthesis but also acts as a stimulus to promote this process. However, the molecular mechanisms underlying sucrose and endosperm filling are poorly understood. In this study, we found that sucrose promotes the expression of endosperm-filling hub gene Opaque2 (O2), coordinating with storage-reserve accumulation. We showed that the protein kinase SnRK1a1 can attenuate O2-mediated transactivation, but sucrose can release this suppression. Biochemical assays revealed that SnRK1a1 phosphorylates O2 at serine 41 (S41), negatively affecting its protein stability and transactivation ability. We observed that mutation of SnRK1a1 results in larger seeds with increased kernel weight and storage reserves, while overexpression of SnRK1a1 causes the opposite effect. Overexpression of the native O2 (O2-OE), phospho-dead (O2-SA), and phospho-mimetic (O2-SD) variants all increased 100-kernel weight. Although O2-SA seeds exhibit smaller kernel size, they have higher accumulation of starch and proteins, resulting in larger vitreous endosperm and increased test weight. O2-SD seeds display larger kernel size but unchanged levels of storage reserves and test weight. O2-OE seeds show elevated kernel dimensions and nutrient storage, like a mixture of O2-SA and O2-SD seeds. Collectively, our study discovers a novel regulatory mechanism of maize endosperm filling. Identification of S41 as a SnRK1-mediated phosphorylation site in O2 offers a potential engineering target for enhancing storage-reserve accumulation and yield in maize. Sucrose promotes O2 expression for endosperm filling, which is attenuated by SnRK1a1 through phosphorylation modification and protein degradation. The sucrose-SnRK1a1-O2 regulatory pathway offers potentials for maize yield and nutrient quality improvement through phosphorylation modification. [ABSTRACT FROM AUTHOR]

The sensor kinase Sucrose Non-fermenting-1-Related Kinase 1 (SnRK1) plays a central role in energy and metabolic homeostasis. KIN10 is a major catalytic (a) kinase subunit of SnRK1 regulated by transcription, posttranslational modification, targeted protein degradation, and its subcellular localization. Geminivirus Rep Interacting Kinase 1 and 2 (GRIK1 and 2) are immediate upstream kinases of KIN10. In the transient protein expression assays carried out in Nicotiana benthamiana (N. benthamiana) leaves, GRIK1 not only phosphorylates KIN10 but also simultaneously initiates its degradation. Posttranslational GRIK-mediated KIN10 degradation is dependent on both GRIK kinase activity and phosphorylation of the KIN10 T-loop. KIN10 proteins are significantly enriched in the grik1-1 grik2-1 double mutant, consistent with the transient assays in N. benthamiana. Interestingly. Among the enriched KIN10 proteins from grik1-1 grik2-1, is a longer isoform, putatively derived by alternative splicing which is barely detectable in wild-type plants. The reduced stability of KIN10 upon phosphorylation and activation by GRIK represents a mechanism that enables the KIN10 activity to be rapidly reduced when the levels of intracellular sugar/energy are restored to their set point, representing an important homeostatic control that prevents a metabolic overreaction to lowsugar conditions. Since GRIKs are activating kinases of KIN10, KIN10s in the grik1 grik2 double null mutant background remain un-phosphorylated, with only their basal level of activity, are more stable, and therefore increase in abundance, which also explains the longer isoform KIN10L which is a minor isoform in wild type is clearly detected in the grik1 grik2 double mutant. [ABSTRACT FROM AUTHOR]

Geminiviruses are a group of single-stranded DNA viruses that have developed multiple strategies to overcome host defenses and establish viral infections. Sucrose nonfermenting-1-related kinase 1 (SnRK1) is a key regulator of energy balance in plants and plays an important role in plant development and immune defenses. As a heterotrimeric complex, SnRK1 is composed of a catalytic subunit α (SnRK1 α) and two regulatory subunits, β and γ. Previous studies on SnRK1 in plant defenses against microbial pathogens have mainly focused on SnRK1 α. In this study, we validated the interaction between the C4 protein encoded by tobacco leaf curl Yunnan virus (TbLCYnV) and the regulatory subunit β of Nicotiana benthamiana SnRK1, i.e., NbSnRK1 β2, and identified that the Asp22 of C4 is critical for TbLCYnV C4–NbSnRK1 β2 interactions. NbSnRK1 β2 silencing in N. benthamiana enhances susceptibility to TbLCYnV infection. Plants infected with viral mutant TbLCYnV (C4D22A), which contains the mutant version C4 (D22A) that is incapable of interacting with NbSnRK1 β2, display milder symptoms and lower viral accumulation. Furthermore, we discovered that C4 promotes NbSnRK1 β2 degradation via the autophagy pathway. We herein propose a model by which the geminivirus C4 protein causes NbSnRK1 β2 degradation via the TbLCYnV C4–NbSnRK1 β2 interaction to antagonize host antiviral defenses and facilitates viral infection and symptom development in N. benthamiana. [ABSTRACT FROM AUTHOR]

Strawberry is a major fruit crop worldwide because its nutritional and health benefits to human health, but its productivity is limited by Botrytis cinerea. Sucrose nonfermentation 1-related protein kinase 1 (SnRK1) has a defense function against pathogens, but the function of SnRK1 in the defense response to B. cinerea in plants is still unclear. In this study, FaSnRK1α-OE and RNAi fruits were constructed and then inoculated with B. cinerea. The result reveals a positive role of FaSnRK1α in the regulation of resistance to gray mold. FaSnRK1α affects SA content by regulating FaPAL1 and FaPAL2 expressions. The genes related to the SA signaling pathway (FaTGA1 and FaTGA2.1) were significantly increased/decreased in FaSnRK1α-OE or FaSnRK1α-RNAi fruit, respectively. FaSnRK1α interacted with the FaWRKY33.2 protein and negatively regulated FaWRKY33.2 expression, and FaWRKY33.2 acts as a repressor of disease resistance to B. cinerea. Finally, FaSnRK1α regulates the expression of six PR genes and the activities of antioxidant enzymes to boost defense response after B. cinerea inoculation. Our findings showed that FaSnRK1α increases the resistance of strawberry fruit to B. cinerea via SA signaling pathway and interaction with the FaWRKY33.2 transcription factor.

A study published in the Journal of Experimental Botany investigated the effects of compound 991, an activator of SnRK1, on seed germination in rice and wheat. The researchers found that compound 991 increased SnRK1 activity and promoted germination at low concentrations in rice seeds. However, higher concentrations of the compound resulted in a reduction in germination rate. Similar effects were observed in wheat. The study also showed that overexpression of OsSnRK1α, the catalytic subunit of SnRK1, induced a similar response to compound 991 treatment. Phosphoproteomic analysis revealed that compound 991 activates the phosphorylation network regulated by SnRK1 during germination. The findings suggest that compound 991 has potential applications in plant growth regulation in agriculture. [Extracted from the article]

Plant roots explore the soil for water and nutrients, thereby determining plant fitness and agricultural yield, as well as determining ground substructure, water levels, and global carbon sequestration. The colonization of the soil requires investment of carbon and energy, but how sugar and energy signaling are integrated with root branching is unknown. Here, we show through combined genetic and chemical modulation of signaling pathways that the sugar small-molecule signal, trehalose-6-phosphate (T6P) regulates root branching through master kinases SNF1-related kinase-1 (SnRK1) and Target of Rapamycin (TOR) and with the involvement of the plant hormone auxin. Increase of T6P levels both via genetic targeting in lateral root (LR) founder cells and through light-activated release of the presignaling T6P-precursor reveals that T6P increases root branching through coordinated inhibition of SnRK1 and activation of TOR. Auxin, the master regulator of LR formation, impacts this T6P function by transcriptionally down-regulating the T6P-degrader trehalose phosphate phosphatase B in LR cells. Our results reveal a regulatory energy-balance network for LR formation that links the 'sugar signal' T6P to both SnRK1 and TOR downstream of auxin. [ABSTRACT FROM AUTHOR]

SUMMARY: Plants have evolved an extensive specialized secondary metabolism. The colorful flavonoid anthocyanins, for example, not only stimulate flower pollination and seed dispersal, but also protect different tissues against high light, UV and oxidative stress. Their biosynthesis is highly regulated by environmental and developmental cues and induced by high sucrose levels. Expression of the biosynthetic enzymes involved is controlled by a transcriptional MBW complex, comprising (R2R3) MYB‐ and bHLH‐type transcription factors and the WD40 repeat protein TTG1. Anthocyanin biosynthesis is not only useful, but also carbon‐ and energy‐intensive and non‐vital. Consistently, the SnRK1 protein kinase, a metabolic sensor activated in carbon‐ and energy‐depleting stress conditions, represses anthocyanin biosynthesis. Here we show that Arabidopsis SnRK1 represses MBW complex activity both at the transcriptional and post‐translational level. In addition to repressing expression of the key transcription factor MYB75/PAP1, SnRK1 activity triggers MBW complex dissociation, associated with loss of target promoter binding, MYB75 protein degradation and nuclear export of TTG1. We also provide evidence for direct interaction with and phosphorylation of multiple MBW complex proteins. These results indicate that repression of expensive anthocyanin biosynthesis is an important strategy to save energy and redirect carbon flow to more essential processes for survival in metabolic stress conditions. Significance Statement: In carbon‐ and energy‐depleting stress conditions, plants need to prioritize and redirect carbon flow from useful but expensive and non‐essential metabolites to more vital processes for metabolic homeostasis and survival. Consistently, the SnRK1 protein kinase represses activity of the MBW complex controlling anthocyanin biosynthesis gene expression, both at the transcriptional and post‐translational level. [ABSTRACT FROM AUTHOR]

SUMMARY: Plants need to integrate internal and environmental signals to mount adequate stress responses. The NUCLEAR PORE COMPLEX (NPC) component HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1 (HOS1) is emerging as such an integrator, affecting responses to cold, heat, light, and salinity. Stress conditions often converge in a low‐energy signal that activates SUCROSE NON‐FERMENTING 1‐RELATED KINASE 1 (SnRK1) to promote stress tolerance and survival. Here, we explored the role of HOS1 in the SnRK1‐dependent response to low‐energy stress in Arabidopsis thaliana, using darkness as a treatment and a combination of genetic, biochemical, and phenotypic assays. We show that the induction of starvation genes and plant tolerance to prolonged darkness are defective in the hos1 mutant. HOS1 interacts physically with the SnRK1α1 catalytic subunit in yeast two‐hybrid assays and in planta, and the nuclear accumulation of SnRK1α1 is reduced in the hos1 mutant. Likewise, another NPC mutant, nup160, exhibits lower activation of starvation genes and decreased tolerance to prolonged darkness. Importantly, defects in low‐energy responses in the hos1 background are rescued by fusing SnRK1α1 to a potent nuclear localization signal or by sugar supplementation during the dark treatment. Altogether, this work demonstrates the importance of HOS1 for the nuclear accumulation of SnRK1α1, which is key for plant tolerance to low‐energy conditions. Significance Statement: The nuclear pore complex component HOS1 has important functions in plant responses to cold, heat, light, and salinity. Here, we show that HOS1 is important for plant tolerance to low‐energy conditions, using darkness as a treatment, and that this is largely due to its involvement in the nuclear accumulation of the energy‐sensing kinase SnRK1. [ABSTRACT FROM AUTHOR]

Sucrose nonfermenting-related protein kinase 1 (SnRK1) is one of the critical serine/threonine protein kinases. It commonly mediates plant growth and development, cross-talks with metabolism processes and physiological responses to biotic or abiotic stresses. It plays a key role in distributing carbohydrates and sugar signal transporting. In the present study, eight SnRK1 coding genes were identified in sorghum (Sorghum bicolor L.) via sequences alignment, with three for α subunits (SnRK1α1 to SnRK1α3), three for β (SnRK1β1 to SnRK1β3), and one for both γ (SnRK1γ) and βγ (SnRK1βγ). These eight corresponding genes located on five chromosomes (Chr) of Chr1–3, Chr7, and Chr9 and presented collinearities to SnRK1s from maize and rice, exhibiting highly conserved domains within the same subunits from the three kinds of cereals. Expression results via qRT-PCR showed that different coding genes of SnRK1s in sorghum possessed similar expression patterns except for SnRK1α3 with a low expression level in grains and SnRK1β2 with a relatively high expression level in inflorescences. Results of subcellular localization in sorghum leaf protoplast showed that SnRK1α1/α2/α3/γ mainly located on organelles, while the rest four of SnRK1β1/β2/β3/βγ located on both membranes and some organelles. Besides, three combinations were discovered among eight SnRK1 subunits in sorghum through yeast two hybrid, including α1-β2-βγ, α2-β3-γ, and α3-β3-γ. These results provide informative references for the following functional dissection of SnRK1 subunits in sorghum.

SnRK1, an evolutionarily conserved heterotrimeric kinase complex that acts as a key metabolic sensor in maintaining energy homeostasis in plants, is an important upstream activator of autophagy that serves as a cellular degradation mechanism for the healthy growth of plants. However, whether and how the autophagy pathway is involved in regulating SnRK1 activity remains unknown. In this study, we identified a clade of plant-specific and mitochondria-localized FCS-like zinc finger (FLZ) proteins as currently unknown ATG8-interacting partners that actively inhibit SnRK1 signaling by repressing the T-loop phosphorylation of the catalytic α subunits of SnRK1, thereby negatively modulating autophagy and plant tolerance to energy deprivation caused by long-term carbon starvation. Interestingly, these AtFLZs are transcriptionally repressed by low-energy stress, and AtFLZ proteins undergo a selective autophagy-dependent pathway to be delivered to the vacuole for degradation, thereby constituting a positive feedback regulation to relieve their repression of SnRK1 signaling. Bioinformatic analyses show that the ATG8-FLZ-SnRK1 regulatory axis first appears in gymnosperms and seems to be highly conserved during the evolution of seed plants. Consistent with this, depletion of ATG8-interacting ZmFLZ14 confers enhanced tolerance, whereas overexpression of ZmFLZ14 leads to reduced tolerance to energy deprivation in maize. Collectively, our study reveals a previously unknown mechanism by which autophagy contributes to the positive feedback regulation of SnRK1 signaling, thereby enabling plants to better adapt to stressful environments. Whether and how the autophagy pathway is involved in regulating the activity of SnRK1, an evolutionarily conserved heterotrimeric kinase complex that acts as a key metabolic sensor in maintaining energy homeostasis in plants, remains unknown. This study reveals that autophagy positively regulates SnRK1 signaling under energy-limiting conditions by mediating the selective autophagic degradation of SnRK1 repressors, termed ATG8-interacting FCS-like zinc finger (FLZ) proteins. [ABSTRACT FROM AUTHOR]

Endodormancy (ED) is a crucial stage in the life cycle of many perennial plants. ED release requires accumulating a certain amount of cold exposure, measured as chilling units. However, the mechanism governing the effect of chilling on ED duration is poorly understood. We used the potato tuber model to investigate the response to chilling as associated with ED release. We measured the accumulation of specific sugars during and after chilling, defined as sugar units. We discovered that ED duration correlated better with sugar units accumulation than chilling units. A logistic function was developed based on sugar units measurements to predict ED duration. Knockout or overexpression of the vacuolar invertase gene (StVInv) unexpectedly modified sugar units levels and extended or shortened ED, respectively. Silencing the energy sensor SNF1‐related protein kinase 1, induced higher sugar units accumulation and shorter ED. Sugar units accumulation induced by chilling or transgenic lines reduced plasmodesmal (PD) closure in the dormant bud meristem. Chilling or knockout of abscisic acid (ABA) 8′‐hydroxylase induced ABA accumulation, in parallel to sweetening, and antagonistically promoted PD closure. Our results suggest that chilling induce sugar units and ABA accumulation, resulting in antagonistic signals for symplastic connection of the dormant bud. Summary statement: Endodormancy (ED) duration of potato tuber correlates better with soluble sugars accumulation (sugar units) than chilling units. Chilling induces sugar units and ABA accumulation, resulting in antagonistic signals for symplastic connection of the dormant bud, determining ED duration. [ABSTRACT FROM AUTHOR]

In plants, SnRK1 (Sucrose non-fermenting-Related protein Kinase 1) is one of the major activators of catabolic processes, including autophagy, during stress responses. SnRK1 generally acts as a sensor of the energy status of the cell. Photosynthesis is by far the largest energy-supplying process in green plant cells exposed to light; thus, SnRK1 might participate in its regulation. In leaves of Arabidopsis lines with different levels of the catalytic subunit of SnRK1, KIN10, quantum yields of photosystems and of non-photochemical quenching, formation of the transthylakoid proton motive force, and contents of ATP in seedlings were compared under optimal conditions and under salinity stress. We detected specific changes in the photochemical activity of the chloroplasts that were assigned to constant activation of SnRK1 in two lines with constitutive overexpression of KIN10, both under control conditions and under salinity stress. Furthermore, the inhibition of the SnRK1 activity by means of RNA interference in Arabidopsis led to a lack of response to salinity at the level of chloroplast photochemistry. [ABSTRACT FROM AUTHOR]

SUMMARY: Quiescence is a crucial survival attribute in which cell division is repressed in a reversible manner. Although quiescence has long been viewed as an inactive state, recent studies have shown that it is an actively monitored process that is influenced by environmental stimuli. Here, we provide a perspective of the quiescent state and discuss how this process is tuned by energy, nutrient and oxygen status, and the pathways that sense and transmit these signals. We not only highlight the governance of canonical regulators and signalling mechanisms that respond to changes in nutrient and energy status, but also consider the central significance of mitochondrial functions and cues as key regulators of nuclear gene expression. Furthermore, we discuss how reactive oxygen species and the associated redox processes, which are intrinsically linked to energy carbohydrate metabolism, also play a key role in the orchestration of quiescence. Significance Statement: The biology of plant quiescence, which makes cells highly resistant to environmental stress, is complex and poorly understood. Recent developments in dissecting the reciprocal influences of cellular energy and redox metabolism and signalling with nuclear controls provide new insights into how this essential process is established and the developmental functions it serves. [ABSTRACT FROM AUTHOR]

Sucrose non-fermenting kinase 1 (SnRK1) has emerged as a pivotal activator of the autophagy pathway; however, the reciprocal influence of autophagy on SnRK1 remains unknown. Yang et al. have recently revealed the existence of a feedback loop connecting autophagy and SnRK1 in terrestrial plants, involving the novel FCS-like zinc finger (FLZ) class of proteins. [ABSTRACT FROM AUTHOR]

Summary: CYCLIN‐DEPENDENT KINASE 8 (CDK8), a component of the kinase module of the Mediator complex in Arabidopsis, is involved in many processes, including flowering, plant defense, drought, and energy stress responses. Here, we investigated cdk8 mutants and CDK8‐overexpressing lines to evaluate whether CDK8 also plays a role in regulating lipid synthesis, an energy‐demanding anabolism.Quantitative lipid analysis demonstrated significant reductions in lipid synthesis rates and lipid accumulation in developing siliques and seedlings of cdk8, and conversely, elevated lipid contents in wild‐type seed overexpressing CDK8. Transactivation assays show that CDK8 is necessary for maximal transactivation of the master seed oil activator WRINKLED1 (WRI1) by the seed maturation transcription factor ABSCISIC ACID INSENSITIVE3, supporting a direct regulatory role of CDK8 in oil synthesis.Thermophoretic studies show GEMINIVIRUS REP INTERACTING KINASE1, an activating kinase of KIN10 (a catalytic subunit of SUCROSE NON‐FERMENTING1‐RELATED KINASE1), physically interacts with CDK8, resulting in its phosphorylation and degradation in the presence of KIN10.This work defines a mechanism whereby, once activated, KIN10 downregulates WRI1 expression and suppresses lipid synthesis via promoting the degradation of CDK8. The KIN10‐CDK8‐dependent regulation of lipid synthesis described herein is additional to our previously reported KIN10‐dependent phosphorylation and degradation of WRI1. [ABSTRACT FROM AUTHOR]

Roots are sensors evolved to simultaneously respond to manifold signals, which allow the plant to survive. Root growth responses, including the modulation of directional root growth, were shown to be differently regulated when the root is exposed to a combination of exogenous stimuli compared to an individual stress trigger. Several studies pointed especially to the impact of the negative phototropic response of roots, which interferes with the adaptation of directional root growth upon additional gravitropic, halotropic or mechanical triggers. This review will provide a general overview of known cellular, molecular and signalling mechanisms involved in directional root growth regulation upon exogenous stimuli. Furthermore, we summarise recent experimental approaches to dissect which root growth responses are regulated upon which individual trigger. Finally, we provide a general overview of how to implement the knowledge gained to improve plant breeding. [ABSTRACT FROM AUTHOR]

Summary: Cellular sugar starvation and/or energy deprivation serves as an important signaling cue for the live cells to trigger the necessary stress adaptation response. When exposed to cellular energy stress (ES) conditions, the plants reconfigure metabolic pathways and rebalance energy status while restricting vegetative organ growth. Despite the vital importance of this ES‐induced growth restriction, the regulatory mechanism underlying the response remains largely elusive in plants.Using plant cell‐ and whole plant‐based functional analyses coupled with extended genetic validation, we show that cellular ES‐activated SNF1‐related protein kinase 1 (SnRK1.1) directly interacts with and phosphorylates E2Fa transcription factor, a critical cell cycle regulator.Phosphorylation of E2Fa by SnRK1.1 leads to its proteasome‐mediated protein degradation, resulting in S‐phase repression and organ growth restriction.Our findings show that ES‐dependently activated SnRK1.1 adjusts cell proliferation and vegetative growth for plants to cope with constantly fluctuating environments. [ABSTRACT FROM AUTHOR]

Chilli leaf curl Ahmedabad virus (ChiLCAV), a begomovirus belonging to the family Geminiviridae, has been reported for its occurrence in India, infecting chilli and tomato plants. The viral proteins associated with ChiLCAV involves in the primary pathogenesis and transmission of the virus by whitefly. Viral protein interactions with host proteins show the dynamics of structural binding and interaction in their infection cycle. At the same time, plants have multiple defence mechanisms against bacterial and viral infections. Secondary metabolites play a significant role in the inborne defence mechanism of plants. Host proteins are also the prime producers of secondary metabolites. In the present study, we evaluated the host protein SnRK1 interaction with all six viral proteins (V1, V2, C1, C2, C3 and C4). Apart from C4, all the other viral proteins showed appreciable binding and interaction with SnRK1. SnRK1 has the regulation mechanism for the accumulation of diterpenoids, secondary metabolites. Flavonoids are secondary metabolites produced by the plant under stress conditions. Further, we studied the binding and interaction of six selected flavonoids produced by Solanaceae family members with all the ChiLCAV proteins. All six selected flavonoids showed considerable binding energy with all viral proteins. Each flavonoid showed high binding energy with different viral proteins. Molecular docking is carried out for both flavonoids and the host protein SnRK1. These in silico interactions and docking studies could be useful for understanding the plants defence mechanism against viral infections at the molecular level. [ABSTRACT FROM AUTHOR]

Roots are sensors evolved to simultaneously respond to manifold signals, which allow the plant to survive. Root growth responses, including the modulation of directional root growth, were shown to be differently regulated when the root is exposed to a combination of exogenous stimuli compared to an individual stress trigger. Several studies pointed especially to the impact of the negative phototropic response of roots, which interferes with the adaptation of directional root growth upon additional gravitropic, halotropic or mechanical triggers. This review will provide a general overview of known cellular, molecular and signalling mechanisms involved in directional root growth regulation upon exogenous stimuli. Furthermore, we summarise recent experimental approaches to dissect which root growth responses are regulated upon which individual trigger. Finally, we provide a general overview of how to implement the knowledge gained to improve plant breeding.

SnRK1 protein kinase plays hub roles in plant carbon and nitrogen metabolism. However, the function of SnRK1 in legume nodulation and symbiotic nitrogen fixation is still elusive. In this study, we identified GmNodH, a putative sulfotransferase, as an interacting protein of GmSnRK1 by yeast two-hybrid screen. The qRT-PCR assays indicate that GmNodH gene is highly expressed in soybean roots and could be induced by rhizobial infection and nitrate stress. Fluorescence microscopic analyses showed that GmNodH was colocalized with GsSnRK1 on plasma membrane. The physical interaction between GmNodH and GmSnRK1 was further verified by using split-luciferase complementary assay and pull-down approaches. In vitro phosphorylation assay showed that GmSnRK1 could phosphorylate GmNodH at Ser193. To dissect the function and genetic relationship of GmSnRK1 and GmNodH in soybean, we co-expressed the wild-type and mutated GmSnRK1 and GmNodH genes in soybean hairy roots and found that co-expression of GmSnRK1/GmNodH genes significantly promoted soybean nodulation rates and the expression levels of nodulation-related GmNF5α and GmNSP1 genes. Taken together, this study provides the first biological evidence that GmSnRK1 may interact with and phosphorylate GmNodH to synergistically regulate soybean nodulation. [ABSTRACT FROM AUTHOR]

Sucrose non-fermenting-1-related protein kinase-1 (SnRK1) and its scaffolding proteins, FCS-like zinc finger proteins (FLZs), are well conserved in land plants and involved in various processes of plant growth and stress responses. Glycyrrhiza inflata Bat. is a widely used licorice species with strong abiotic stress resistance, in which terpenoids and flavonoids are the major bioactive components. Here, we identified 2 SnRK1 catalytic α subunit encoding genes (GiSnRK1α1 and GiSnRK1α2) and 21 FLZ genes in G. inflata. Polygenetic analysis showed that the 21 GiFLZs could be divided into three groups. A total of 10 representative GiFLZ proteins interact with GiSnRK1α1, and they display overlapped subcellular localization (mainly in the nucleus and the cytoplasm) when transiently expressed in Nicotiana benthamiana leaf cells. Coinciding with the existence of various phytohormone-responsive and stress-responsive cis-regulatory elements in the GiSnRK1α and GiFLZ gene promoters, GiFLZs are actively responsive to methyl jasmonic acid (MeJA) and abscisic acid (ABA) treatments, and several GiFLZs and GiSnRK1α1 are regulated by drought and saline-alkaline stresses. Interestingly, GiSnRK1α and 20 of 21 GiFLZs (except for GiFLZ2) show higher expression in the roots than in the leaves. These data provide comprehensive information on the SnRK1 catalytic α subunit and the FLZ proteins in licorice for future functional characterization. [ABSTRACT FROM AUTHOR]

In plants, transitory starch is synthetized during the day and degraded at night to provide the continuous carbon needed for growth and development. Starch metabolism is highly coordinated, as the starch degradation rate must be coupled to the amount of starch synthetized during the day. Maltose is one of the chloroplastic products obtained from starch degradation, and maltose is exported to the cytosol where disproportionating enzyme-2 (DPE2) is responsible for its metabolism. The amount of DPE2 remained unchanged throughout the day, but its activity notably increased at the end of the day (7 p.m.), suggesting that posttranslational modification drives the mechanism underlying the regulatory activity of this enzyme. Sucrose nonfermenting-related kinase-1 (SnRK1), a protein kinase that controls the activity of several metabolic enzymes, was able to interact and phosphorylate DPE2 at three different residues localized in the α-glucanotransferase domain. This phosphorylation acts as a positive regulator of DPE2, increasing its activity. Complementation of dpe2- deficient mutants with the wild-type (WT) and S786A forms of DPE2 showed that the nonphosphorylated form of DPE2 only partially restored starch degradation, suggesting that phosphorylation at S786 is involved in enzyme regulation. The model suggests that SnRK1 is activated at night by the maltose that is produced during leaf starch degradation. Activated SnRK1 binds and phosphorylates DPE2 increasing its activity. In this way, the flow of carbon is driven toward the formation of sucrose. [Display omitted] • SnRK1 phosphorylates DPE2. • Phosphorylation of DPE2 increases its enzyme activity. • SnRK1 and DPE2 interact in vivo • Complementation of dpe2 mutants with a nonphosphorylated form of DPE2 recovers a partial starch degradation phenotype. [ABSTRACT FROM AUTHOR]

Taken together the findings presented in this special issue strengthened the role of TORC1 as a signalling hub where multiple signals (e.g. nutrient and phytohormone levels, time of the day and season, light quality) are integrated to ensure temporal and spatial adjustment of plant growth and development by regulating a diverse range of specific effectors and targets. Growth-promoting phytohormones (e.g. auxin, brassinosteroids, and gibberellins) are generally associated with high TORC1 activity, but the opposite is true for growth-restrictive hormones, for which a mutually inhibitory relationship with TORC1 has been described (e.g. ABA, ethylene, and JA). TOR kinase, a GPS in the complex nutrient and hormonal signaling networks to guide plant growth and development. Keywords: TORC1; SnRK1; plant growth; phytohormones; metabolism; translation regulation; autophagy; development; nutrients; carbon partitioning; microalgae EN TORC1 SnRK1 plant growth phytohormones metabolism translation regulation autophagy development nutrients carbon partitioning microalgae 6987 6992 6 11/22/22 20221115 NES 221115 B Twenty years have passed since the identification of the target of rapamycin (TOR) protein kinase in Arabidopsis. [Extracted from the article]

SUCROSE NON-FERMENTING1 (SNF1)-RELATED KINASE 1 (SnRK1) is an evolutionarily conserved protein kinase with key roles in plant stress responses. SnRK1 is activated when energy levels decline during stress, reconfiguring metabolism and gene expression to favour catabolism over anabolism, and ultimately to restore energy balance and homeostasis. The capacity to efficiently redistribute resources is crucial to cope with adverse environmental conditions and, accordingly, genetic manipulations that increase SnRK1 activity are generally associated with enhanced tolerance to stress. In addition to its well-established function in stress responses, an increasing number of studies implicate SnRK1 in the homeostatic control of metabolism during the regular day–night cycle and in different organs and developmental stages. Here, we review how the genetic manipulation of SnRK1 alters central metabolism in several plant species and tissue types. We complement this with studies that provide mechanistic insight into how SnRK1 modulates metabolism, identifying changes in transcripts of metabolic components, altered enzyme activities, or direct regulation of enzymes or transcription factors by SnRK1 via phosphorylation. We identify patterns of response that centre on the maintenance of sucrose levels, in an analogous manner to the role described for its mammalian orthologue in the control of blood glucose homeostasis. Finally, we highlight several knowledge gaps and technical limitations that will have to be addressed in future research aiming to fully understand how SnRK1 modulates metabolism at the cellular and whole-plant levels. [ABSTRACT FROM AUTHOR]

Trehalose 6-phosphate (T6P), the intermediate of trehalose biosynthesis and a signaling molecule, affects crop yield via targeting sucrose allocation and utilization. As there have been no reports of T6P signaling affecting secondary metabolism in a crop plant, the rubber tree Hevea brasiliensis serves as an ideal model in this regard. Sucrose metabolism critically influences the productivity of natural rubber, a secondary metabolite of industrial importance. Here, we report on the characterization of the T6P synthase (TPS) gene family and the T6P/SNF1-related protein kinase1 (T6P/SnRK1) signaling components in Hevea laticifers under tapping (rubber harvesting), an agronomic manipulation that itself stimulates rubber production. A total of fourteen TPS genes were identified, among which a class II TPS gene, HbTPS5, seemed to have evolved with a function specialized in laticifers. T6P and trehalose increased when the trees were tapped, this being consistent with the observed enhanced activities of TPS and T6P phosphatase (TPP) and expression of an active TPS-encoding gene, HbTPS1. On the other hand, SnRK1 activities decreased, suggesting the inhibition of elevated T6P on SnRK1. Expression profiles of the SnRK1 marker genes coincided with elevated T6P and depressed SnRK1. Interestingly, HbTPS5 expression decreased significantly with the onset of tapping, suggesting a regulatory function in the T6P pathway associated with latex production in laticifers. In brief, transcriptional, enzymatic, and metabolic evidence supports the participation of T6P/SnRK1 signaling in rubber formation, thus providing a possible avenue to increasing the yield of a valuable secondary metabolite by targeting T6P in specific cells. [ABSTRACT FROM AUTHOR]

Understanding how crop varieties acclimate to elevated temperatures is key to priming them for future climates. Here, we exposed two genotypes of Sorghum bicolor (one sensitive to heat shock (Sen) and one tolerant (Tol)) from multiple growth temperatures to a six-day heat shock (reaching 45°C), carrying out a suite of measurements before and during heat shock. Sen consistently reduced photosynthetic functioning during heat shock, while Tol increased its photosynthetic rate. Higher abundance of heat shock protein transcripts and metabolites related to heat tolerance were noted for Tol when compared to Sen both before and during heat shock, which can be attributed to constitutive and inducible responses to elevated temperatures. In addition, important changes in metabolic pathways were clearly identified for Tol during heat shock (including upregulation of raffinose family oligosaccharides and downregulation of the GABA catalytic pathway), even as the concentration of hexose sugars became depleted. We infer Tol was able to tolerate elevated temperatures due to an upregulation of osmoprotectants, chaperones and reactive oxygen species scavengers and by the suppression of SnRK1 via transcripts and metabolites during heat shock. Our results highlight potential targets for attributes of high temperature tolerance which can be utilised in future breeding trials., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Plants have evolved multiple strategies to cope with rapid changes in the environment. During high light (HL) acclimation, the biosynthesis of photoprotective flavonoids, such as anthocyanins, is induced. However, the exact nature of the signal and downstream factors for HL induction of flavonoid biosynthesis (FB) is still under debate. Here, we show that carbon fixation in chloroplasts, subsequent export of photosynthates by triose phosphate/phosphate translocator (TPT), and rapid increase in cellular sugar content permit the transcriptional and metabolic activation of anthocyanin biosynthesis during HL acclimation. In combination with genetic and physiological analysis, targeted and whole-transcriptome gene expression studies suggest that reactive oxygen species and phytohormones play only a minor role in rapid HL induction of the anthocyanin branch of FB. In addition to transcripts of FB, sugar-responsive genes showed delayed repression or induction in tpt-2 during HL treatment, and a significant overlap with transcripts regulated by SNF1-related protein kinase 1 (SnRK1) was observed, including a central transcription factor of FB. Analysis of mutants with increased and repressed SnRK1 activity suggests that sugar-induced inactivation of SnRK1 is required for HL-mediated activation of anthocyanin biosynthesis. Our study emphasizes the central role of chloroplasts as sensors for environmental changes as well as the vital function of sugar signaling in plant acclimation.

Viruses often usurp host machineries for their amplification, but it remains unclear if hosts may subvert virus proteins to regulate viral proliferation. Here, we show that the 17K protein, an important virulence factor conserved in barley yellow dwarf viruses (BYDVs) and related poleroviruses, is phosphorylated by host GRIK1‐SnRK1 kinases, with the phosphorylated 17K (P17K) capable of enhancing the abundance of virus‐derived small interfering RNAs (vsiRNAs) and thus antiviral RNAi. Furthermore, P17K interacts with barley small RNA‐degrading nuclease 1 (HvSDN1) and impedes HvSDN1‐catalyzed vsiRNA degradation. Additionally, P17K weakens the HvSDN1‐HvAGO1 interaction, thus hindering HvSDN1 from accessing and degrading HvAGO1‐carried vsiRNAs. Importantly, transgenic expression of 17K phosphomimetics (17K5D), or genome editing of SDN1, generates stable resistance to BYDV through elevating vsiRNA abundance. These data validate a novel mechanism that enhances antiviral RNAi through host subversion of a viral virulence protein to inhibit SDN1‐catalyzed vsiRNA degradation and suggest new ways for engineering BYDV‐resistant crops. Synopsis: Viruses often subvert host proteins for their amplification, but host subversion of virus proteins to regulate viral proliferation has not been reported in plants. This work shows that a plant‐viral virulence protein is phosphorylated by host kinases, with the phosphorylated form becoming an inhibitor of AGO1‐associated vsiRNAs cleavage and thus enhancing the abundance of antiviral RNAi.The 17K protein of barley yellow dwarf virus (BYDV) is phosphorylated by host GRIK1‐SnRK1 kinases.The phosphorylated 17K (P17K) interacts with host small RNA degrading nuclease 1 (HvSDN1) and Argonaute 1 (HvAGO1), and binds BYDV vsiRNA.P17K inhibits the cleavage of HvAGO1‐associated vsiRNAs by HvSDN1, thus elevating vsiRNA abundance and resulting in enhanced antiviral RNAi.Transgenic expression of a 17K phosphomimetic (17K5D), or genome editing of SDN1, generates stable resistance to BYDV through elevating vsiRNA abundance. [ABSTRACT FROM AUTHOR]

Autophagy is a highly conserved quality control process that maintains cellular health by eliminating deleterious cargoes. Compared with the extensive studies in yeast and mammalian models, the molecular details and significance of post‐translational modifications (PTMs) in the autophagy process in plants remain less well defined. In this review, we discuss recent progress in our understanding of phosphorylation, one of the most extensively studied PTMs, in the regulation of autophagosome biogenesis and autophagic degradation in plants. Based on the plant mass spectrometric database, we summarize the experimentally verified phosphorylation sites of the core autophagy machinery in plants. Furthermore, we put forward several approaches to test the roles of phosphorylation in the regulation of plant autophagy. [ABSTRACT FROM AUTHOR]

Sucrose non-fermenting-1-related protein kinase 1 (SnRK1) plays a key role in rice germination. The small molecule drug, A-769662, activates AMP-activated protein kinase, a mammalian homolog of SnRK1. However, it is unknown whether A-769662 activates SnRK1, thereby affecting germination. SnRK1 in desalted extracts from germinating rice seeds was strongly activated by adding A-769662 in vitro. Applying 50 or 100 μM A-769662 accelerated germination and increased the root length, shoot length, and seedling fresh weight. 50 μM A-769662 treatment increased the catalytic activity and phosphorylation of SnRK1 during germination. Transcriptome analysis and biochemical validation were performed to investigate the mechanism whereby A-769662 treatment promoted rice germination. A-769662 treatment promoted starch hydrolysis by increasing the expression and activity of amylase and inhibited starch biosynthesis by decreasing the expression of OsAGPL2 , OsAGPS2a , Wx , and SSIIa. The abscisic acid (ABA) level and gene expression of ABA-induced transcription factors, including OsNF-YC9 , OsNF-YC12 , OsWRKY24 , OsPYL8 , OsMKKK62 , and OsMKKK63 , which reduced the inhibition of germination by ABA were decreased under 50 μM A-769662 treatment. The increased expression of the OsACO3 and OsACO5 genes and increased ethylene levels under A-769662 treatment, which counteracted the inhibition of ABA on germination and, thus, promoted germination. These results demonstrate the activation of A-769662 on SnRK1 and further reveal the regulatory mechanism of A-769662 in rice seed germination and nutrient remobilization. • AMPK activator, A-769662, strongly increases SnRK1 activity in vitro. • A-769662 treatment accelerates germination by affecting amylase gene expression, ABA pathway and ethylene biosynthesis. • SnRK1 may alter T6P level by regulating expression of TPP genes. [ABSTRACT FROM AUTHOR]

In plants, oxidative stress and metabolic reprogramming frequently induce male sterility, however our knowledge of the underlying molecular mechanism is far from complete. Here, a maize genic male-sterility (GMS) mutant (ms33-6038) with a loss-of-function of the ZmMs33 gene encoding glycerol-3-phosphate acyltransferase 6 (GPAT6) displayed severe deficiencies in the development of a four-layer anther wall and microspores and excessive reactive oxygen species (ROS) content in anthers. In ms33-6038 anthers, transcriptome analysis identified thousands of differentially expressed genes that were functionally enriched in stress response and primary metabolism pathways. Further investigation revealed that 64 genes involved in ROS production, scavenging, and signaling were specifically changed in expression levels in ms33-6038 anthers compared to the other five investigated GMS lines. The severe oxidative stress triggered premature tapetal autophagy and metabolic reprogramming mediated mainly by the activated SnRK1-bZIP pathway, as well as the TOR and PP2AC pathways, proven by transcriptome analysis. Furthermore, 20 reported maize GMS genes were altered in expression levels in ms33-6038 anthers. The excessive oxidative stress and the metabolic reprogramming resulted in severe phenotypic deficiencies in ms33-6038 anthers. These findings enrich our understanding of the molecular mechanisms by which ROS and metabolic homeostasis impair anther and pollen development in plants. [ABSTRACT FROM AUTHOR]

Sugar is involved in initiating leaf senescence. However, its regulatory role, especially as a signal in the senescence process, is unclear. Therefore, this study was designed to illustrate how sugar stimulates the onset of leaf senescence and controls sugar homeostasis through the T6P-SnRK (sucrose non-fermenting (SNF)-related kinase) and HXK (hexokinase) signaling pathways. We used a leaf disc system detached from fully expanded leaves of Nicotiana tabacum cv. K326 and designed a time-course study (days 3, 5, 7, and 9) with exogenously gradient concentrations (0, 30, 60, 90, 120, and 150 mM) of sucrose (Suc) treatment to identify how Suc application affects sugar metabolism and induces senescence. Our results revealed that early decreases of Fv/Fm and increases in electrolyte leakage responded to Suc on day 3. Furthermore, a substantial increase in lipid peroxidation and up-regulated expression of senescence marker genes (NtSAG12) (except 60 mM on day 3) responded sequentially by day 5. The glucose, G6P, and HXK contents were first induced by Suc on day 3 and then repressed from day 5 to day 7. However, exogenous Suc treatment significantly improved the TPS content and the subsequent precursor T6P from day 3 to day 7. Following exogenous Suc treatments, the transcript level of NtSnRK1 was markedly down-regulated from day 3 to day 7. On the other hand, a linear regression analysis demonstrated that the T6P- NtSnRK1 signaling pathway was strongly associated with senescence initiation, and was accompanied by membrane degradation and NtCP1 / NtSAG12 up-regulation by day 3. The T6P- NtSnRK1 signaling pathway experienced membrane and chloroplast degradation by day 5. HXK functioned as a metabolic enzyme promoting Glc-G6P and as a Glc sensor, accelerating the initiation of senescence through the HXK-dependent pathway by repressing PSII by day 3 and the senescence process through the Glycolytic pathway by day 7. These physiological, biochemical, and molecular analyses demonstrate that exogenous Suc regulates T6P accumulation, inducing senescence through the NtSnRK signaling pathway. These results illustrate the role of Suc and the transition of the sugar signaling pathway during the progression of senescence initiation. • Sucrose uptake activates the Glc-G6P-T6P metabolic pathway throughout the time points in the detached leaf disc. • T6P's accumulation suppressed SnRK1 expression gradually during the senescence initiation to progression • Hexokinase dependent pathway is activated earlier, and the glycolytic pathway is activated later in senescence progression. • Suc has been proven to induce senescence by T6P-SnRK1 signaling pathway in the N. tabacum detached leaf discs. [ABSTRACT FROM AUTHOR]

Sucrose (Suc) accumulation is one of the key indicators of leaf senescence onset, but little is known about its regulatory role. Here, we found that application of high (120–150 mM) and low levels (60 mM) of Suc to young leaf (YL) and fully expanded leaf (FEL) discs, respectively, decreased chlorophyll content and maximum photosynthetic efficiency. Electrolyte leakage and malondialdehyde levels increased at high Suc concentrations (90–120 mM in YL and 60 and 150 mM in FEL discs). In FEL discs, the senescence-associated gene NtSAG12 showed a gradual increase in expression with increased Suc application; in contrast, in YL discs, NtSAG12 was upregulated with low Suc treatment (60 mM) but downregulated at higher levels of Suc. In YL discs, trehalose-6-phosphate (T6P) accumulated at a low half-maximal effective concentration (EC50) of Suc (1.765 mM). However, T6P levels declined as trehalose 6 phosphate synthase (TPS) content decreased, resulting in the maximum velocity of sucrose non-fermenting-1-related protein kinase (SnRK) and hexokinase (HXK) occurring at higher level of Suc. We therefore speculated that senescence was induced by hexose accumulation. In FEL discs, the EC50 of T6P occurred at a low concentration of Suc (0.9488 mM); T6P levels progressively increased with higher TPS content, which inhibited SnRK activity with a dissociation constant (Kd) of 0.001475 U/g. This confirmed that the T6P–SnRK complex induced senescence in detached FEL discs. [ABSTRACT FROM AUTHOR]

Genome targeting with CRISPR/Cas9 is a popular method for introducing mutations and creating knock-out effects. However, limited information is currently available on the mutagenesis of essential genes. This study investigated the efficiency of CRISPR/Cas9 in targeting rice essential genes: the singleton TARGET OF RAPAMYCIN (OsTOR) and the three paralogs of the Sucrose non-fermenting-1 (SNF1)-related kinase 1 (OsSnRK1α), OsSnRK1αA, OsSnRK1αB and OsSnRK1αC. Strong activity of constitutively expressed CRISPR/Cas9 was effective in creating mutations in OsTOR and OsSnRK1α genes, but inducible CRISPR/Cas9 failed to generate detectable mutations. The rate of OsTOR mutagenesis was relatively lower and only the kinase domain of OsTOR could be targeted, while mutations in the HEAT region were unrecoverable. OsSnRK1α paralogs could be targeted at higher rates; however, sterility or early senescence was observed in >50% of the primary mutants. Additionally, OsSnRK1αB and OsSnRK1αC, which bear high sequence homologies, could be targeted simultaneously to generate double-mutants. Further, although limited types of mutations were found in the surviving mutants, the recovered lines displayed loss-of-function or knockdown tor or snrk1 phenotypes. Overall, our data show that mutations in these essential genes can be created by CRISPR/Cas9 to facilitate investigations on their roles in plant development and environmental response in rice. [ABSTRACT FROM AUTHOR]

Plants suffer from a variety of environmental stresses during their growth and development. The evolutionarily conserved sucrose nonfermenting kinase 1-related protein kinase 1 (SnRK1) plays a central role in the regulation of energy homeostasis in response to stresses. In plant cells, autophagy is a degradation process occurring during development or under stress, such as nutrient starvation. In recent years, SnRK1 signaling has been reported to be an upstream activator of autophagy. However, these studies all focused on the regulatory effect of SnRK1 on TOR signaling and the autophagy-related gene 1 (ATG1) complex. In this study, overexpression of the gene encoding the Prunus persica SnRK1 α subunit (PpSnRK1α) in tomato improved the photosynthetic rates and enhanced the resistance to low nutrient stress (LNS). Overexpression of PpSnRK1α increased autophagy activity and upregulated the expression of seven autophagy-related genes (ATGs). The transcriptional levels of SlSnRK2 family genes were altered significantly by PpSnRK1α, signifying that PpSnRK1α may be involved in the ABA signaling pathway. Further analysis showed that PpSnRK1α not only activated autophagy by inhibiting target of rapamycin (TOR) signaling but also enhanced ABA-induced autophagy. This indicates that PpSnRK1α regulates the photosynthetic rate and induces autophagy, and then responds to low nutrient stress. [ABSTRACT FROM AUTHOR]

In plant cells the homeostatic control of energy balance involves the production and recycling of adenylates with macroergic bonds, ATP and ADP. The maintenance of anabolic processes requires the relative saturation of the adenylate pool with high energy phosphoanhydride bonds. The bulk of ATP synthesis is carried out both in mitochondria and in chloroplasts while optimal ATP levels within other cell compartments are maintained by adenylate kinases (AK). AK activity was recently found in cytosol, mitochondria, plastids and the nucleus. ATP synthesis in energy-producing organelles, as well as redistribution of nutrients among cellular compartments, requires fine-tuned regulation of ion homeostasis. A special role in energy metabolism is played by autophagy, a process of active degradation of unwanted and/or damaged cell components and macromolecules within the central lytic vacuole. So-called constitutive autophagy controls the quality of cellular contents under favorable conditions, i.e., when the cellular energy status is high. Energy depletion can lead to the activation of the pro-survival process of autophagic removal and utilization of damaged structures; the breakdown products are then used for ATP regeneration and de novo synthesis of macromolecules. Mitophagy and chlorophagy maintain the populations of healthy and functional energy-producing "stations", preventing accumulation of defective mitochondria and chloroplasts as potential sources of dangerous reactive oxygen species. However, the increase of autophagic flux above a threshold level can lead to the execution of the vacuolar type of programmed cell death (PCD). In this case autophagy also contributes to preservation of energy through support of the outflow of nutrients from dying cells to healthy neighboring tissues. In plants, two central protein kinases, SnRK1 (Snf1-related protein kinase 1) and TOR (target of rapamycin), are responsible for the regulation of the metabolic switch between anabolic and catabolic pathways. TOR promotes the energy-demanding metabolic reactions in response to nutrient availability and simultaneously suppresses catabolism including autophagy. SnRK1, the antagonist of TOR, senses a decline in cellular energy supply and reacts by inducing autophagy through several independent pathways. Here, we provide an overview of the recent knowledge about the interplay between SnRK1 and TOR, autophagy and PCD in course of the regulation of energy balance in plants. [ABSTRACT FROM AUTHOR]

Summary: In Arabidopsis, the differentiation of epidermal cells into stomata is regulated by endogenous and environmental signals. Sugar is required for plant epidermal cell proliferation and differentiation. However, it is unclear how epidermal cells maintain division and differentiation to generate proper amounts of stomata in response to different sugar availability.Here, we show that two evolutionarily conserved kinase Snf1‐related protein kinase 1 (SnRK1) and Target of rapamycin (TOR) play critical roles in the regulation of stomatal development under different sugar availability.When plants are grown on a medium containing 1% sucrose, sucrose‐activated TOR promotes the stomatal development by inducing the expression of SPEECHLESS (SPCH), a master regulator of stomatal development. SnRK1 promotes stomatal development through phosphorylating and stabilizing SPCH. However, under the high sucrose conditions, the highly accumulated trehalose‐6‐phosphate (Tre6P) represses the activity of KIN10, the catalytic α‐subunit of SnRK1, by reducing the interaction between KIN10 and its upstream kinase, consequently promoting SPCH degradation and inhibiting stomatal development.Our findings revealed that TOR and SnRK1 finely regulate SPCH expression and protein stability to optimize the stomatal development in response to exogenously supplied sugar. [ABSTRACT FROM AUTHOR]

The conversion of solar energy to chemical energy by plants during the photosynthetic process provides the main support of the life on the planet. The final products of photosynthesis are carbon skeletons (i.e sugars) that result of the atmospheric CO2 fixation in the leaves and that are the main food and energy source for plants. Throughout evolution, sugars served not only as a source of energy, but also as signaling molecules that communicate the variations of the energetic status in the plant through the participation of various extracellular and intracellular protein receptors. Diverse monosaccharides (glucose and fructose) and disaccharides (sucrose and trehalose) trigger different signaling pathways that involve the participation of kinases and transcription factors that modulate the expression of hundreds of nuclear genes required for plant growth, development, and stress responses. The goal of this review is to provide an overview of how sugars are produced, their transport in the plant, as well as the current knowledge on the perception and signaling processes mediated by these compounds that impact throughout the entire life of the plants. [ABSTRACT FROM AUTHOR]

Nutrients are vital to life through intertwined sensing, signaling, and metabolic processes. Emerging research focuses on how distinct nutrient signaling networks integrate and coordinate gene expression, metabolism, growth, and survival. We review the multifaceted roles of sugars, nitrate, and phosphate as essential plant nutrients in controlling complex molecular and cellular mechanisms of dynamic signaling networks. Key advances in central sugar and energy signaling mechanisms mediated by the evolutionarily conserved master regulators HEXOKINASE1 (HXK1), TARGET OF RAPAMYCIN (TOR), and SNF1-RELATED PROTEIN KINASE1 (SNRK1) are discussed. Significant progress in primary nitrate sensing, calcium signaling, transcriptome analysis, and root–shoot communication to shape plant biomass and architecture are elaborated. Discoveries on intracellular and extracellular phosphate signaling and the intimate connections with nitrate and sugar signaling are examined. This review highlights the dynamic nutrient, energy, growth, and stress signaling networks that orchestrate systemwide transcriptional, translational, and metabolic reprogramming, modulate growth and developmental programs, and respond to environmental cues. [ABSTRACT FROM AUTHOR]

Sucrose non-fermenting-related protein kinase 1 (SnRK1) belongs to a plant serine/threonine protein kinase family, and is part of a large interactive network of signaling pathways in plants to regulate many aspects of growth and development, and its gene expressions are highly responsive to multiple external stimuli. To functionally characterize the role of different SnRK1 members in wild soybean and identify the expression patterns of novel SnRK1 promoters for transgenic research, in this study, we performed an in silico analysis of the SnRK1 gene family in wild soybean and found GsSnRK1.1 and GsSnRK1.2 are main SnRK1 isoforms in wild soybean. The promoter fragments of both GsSnRK1.1 and GsSnRK1.2 were isolated, and a series of 5′-deletion and the full-length versions of both GsSnRK1.1 and GsSnRK1.2 promoters were fused with GUS reporter gene to generate expression vectors. The GUS activities in different tissues of seedling and adult growth stages of transgenic Arabidopsis plants were determined, and the GUS activities in transgenic Arabidopsis plants under NaCl, NaHCO3, PEG, ABA, MeJA and SA were also analyzed. The results showed that GsSnRK1.1 and GsSnRK1.2 genes have different expression patterns and both promoters may contain enhancers and silencers. In addition, NaCl, NaHCO3, ABA, MeJA, and PEG treatments enhanced, whereas SA treatment decreased the GUS activity under the control of both GsSnRK1.1 and GsSnRK1.2 promoters, which may be due to the distributions of various cis-elements in both GsSnRK1.1 and GsSnRK1.2 promoter regions. These results will contribute to a better understanding of the underlying mechanisms of GsSnRK1 genes in response to various abiotic stresses, and as stress-inducible promoters, GsSnRK1.1 and GsSnRK1.2 promoters can be candidates for practical application in agriculture. [ABSTRACT FROM AUTHOR]

Plants adjust their energy metabolism to continuous environmental fluctuations, resulting in a tremendous plasticity in their architecture. The regulatory circuits involved, however, remain largely unresolved. In Arabidopsis, moderate perturbations in photosynthetic activity, administered by short-term low light exposure or unexpected darkness, lead to increased lateral root (LR) initiation. Consistent with expression of low-energy markers, these treatments alter energy homeostasis and reduce sugar availability in roots. Here, we demonstrate that the LR response requires the metabolic stress sensor kinase Snf1-RELATED-KINASE1 (SnRK1), which phosphorylates the transcription factor BASIC LEUCINE ZIPPER63 (bZIP63) that directly binds and activates the promoter of AUXIN RESPONSE FACTOR19 (ARF19), a key regulator of LR initiation. Consistently, starvation-induced ARF19 transcription is impaired in bzip63 mutants. This study highlights a positive developmental function of SnRK1. During energy limitation, LRs are initiated and primed for outgrowth upon recovery. Hence, this study provides mechanistic insights into how energy shapes the agronomically important root system. [ABSTRACT FROM AUTHOR]

The Snf1-related protein kinase 1 (SnRK1) is the plant homolog of the heterotrimeric AMP-activated protein kinase/sucrose non-fermenting 1 (AMPK/Snf1), which works as a major regulator of growth under nutrient-limiting conditions in eukaryotes. Along with its conserved role as a master regulator of sugar starvation responses, SnRK1 is involved in controlling the developmental plasticity and resilience under diverse environmental conditions in plants. In this review, through mining and analyzing the interactome and phosphoproteome data of SnRK1, we are highlighting its role in fundamental cellular processes such as gene regulation, protein synthesis, primary metabolism, protein trafficking, nutrient homeostasis, and autophagy. Along with the well-characterized molecular interaction in SnRK1 signaling, our analysis highlights several unchartered regions of SnRK1 signaling in plants such as its possible communication with chromatin remodelers, histone modifiers, and inositol phosphate signaling. We also discuss potential reciprocal interactions of SnRK1 signaling with other signaling pathways and cellular processes, which could be involved in maintaining flexibility and homeostasis under different environmental conditions. Overall, this review provides a comprehensive overview of the SnRK1 signaling network in plants and suggests many novel directions for future research. [ABSTRACT FROM AUTHOR]