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Salinity is a significant threat that causes considerable yield losses in date palm. The root endophytic fungus Piriformospora indica has proven effective in providing salt stress tolerance to host plants. However, the underlying molecular mechanism facilitating the date palm's response to P. indica inoculation, and its involvement in the salt stress tolerance, remains unknown. In this study, the colonization of P. indica on date palm seedlings exposed to saline conditions was observed through confocal microscopy, and its impact on gene expressions was evaluated using the transcriptomic analysis. Our findings show that P. indica colonization reinforced the cortical cells, prevented them from plasmolysis and cell death under salinity. The RNAseq analysis produced clean reads ranging from 62,040,451 to 3,652,095 across the treatment groups, successfully assembling into 30,600 annotated genes. Out of them, the number of differentially expressed genes (DEGs) varied across the treatments: i.e., 2523, 2031, and 1936 DEGs were upregulated, while 2323, 959, and 3546 were downregulated in Salt, Fungi, and Fungi+Salt groups, respectively. Furthermore, principal component analysis based on transcriptome profiles revealed discrete clustering of samples from different treatment groups. KEGG and GO pathways enrichment analysis highlighted variation in the number and types of enriched pathways among the treatments. Our study indicated variations in gene expression related to plant hormone biosynthesis and signal transduction (auxin, abscisic acid, gibberellin, and ethylene), ABC transporters, sodium/hydrogen exchanger, cation HKT transporter, transcription factors such as WRKY and MYBs, and the plant immune system (lipoxygenase and jasmonate) of the date palm seedlings. By characterizing the transcriptome of date palm roots under salt stress and with colonization of P. indica, the present findings provide valuable perspectives on the molecular mechanisms responsible for inducing salinity stress tolerance in plants. [ABSTRACT FROM AUTHOR]

The INDETERMINATE DOMAIN (IDD) family belongs to a group of plant-specific transcription factors that coordinates plant growth/development and immunity. However, the function and mode of action of IDDs during abiotic stress, such as salt, are poorly understood. We used idd4 transgenic lines and screened them under salt stress to find the involvement of IDD4 in salinity stress tolerance The genetic disruption of IDD4 increases salt-tolerance, characterized by sustained plant growth, improved Na+/K+ ratio, and decreased stomatal density/aperture. Yet, IDD4 overexpressing plants were hypersensitive to salt-stress with an increase in stomatal density and pore size. Transcriptomic and ChIP-seq analyses revealed that IDD4 directly controls an important set of genes involved in abiotic stress/salinity responses. Interestingly, using anti-IDD4-pS73 antibody we discovered that IDD4 is specifically phosphorylated at serine-73 by MPK6 in vivo under salinity stress. Analysis of plants expressing the phosphodead and phospho-mimicking IDD4 versions proved that phosphorylation of IDD4 plays a crucial role in plant transcriptional reprogramming of salt-stress genes. Altogether, we show that salt stress adaption involves MPK6 phosphorylation of IDD4 thereby regulating IDD4 DNA-binding and expression of target genes. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) regulate many developmental processes, including shoot-branching/tillering, and mediate rhizospheric interactions. SLs originate from carlactone (CL) and are structurally diverse, divided into a canonical and a noncanonical subfamily. Rice contains two canonical SLs, 4-deoxyorobanchol (4DO) and orobanchol (Oro), which are common in different plant species. The cytochrome P450 OsMAX1-900 forms 4DO from CL through repeated oxygenation and ring closure, while the homologous enzyme OsMAX1-1400 hydroxylates 4DO into Oro. To better understand the biological function of 4DO and Oro, we generated CRISPR/Cas9 mutants disrupted in OsMAX1-1400 or in both OsMAX1-900 and OsMAX1-1400. The loss of OsMAX1-1400 activity led to a complete lack of Oro and an accumulation of its precursor 4DO. Moreover, Os1400 mutants showed shorter plant height, panicle and panicle base length, but no tillering phenotype. Hormone quantification and transcriptome analysis of Os1400 mutants revealed elevated auxin levels and changes in the expression of auxin-related, as well as of SL biosynthetic genes. Interestingly, the Os900/1400 double mutant lacking both Oro and 4DO did not show the observed Os1400 architectural phenotypes, indicating their being a result of 4DO accumulation. Treatment of wild-type plants with 4DO confirmed this assumption. A comparison of the Striga seed germinating activity and the mycorrhization of Os900, Os900/1400, and Os1400 loss-of-function mutants demonstrated that the germination activity positively correlates with 4DO content while disrupting OsMAX1-1400 has a negative impact on mycorrhizal symbiosis. Taken together, our paper deciphers the biological function of canonical SLs in rice and reveals their particular contributions to establishing architecture and rhizospheric communications. [ABSTRACT FROM AUTHOR]

Summary: MAPKs are universal eukaryotic signaling factors whose functioning is assumed to depend on the recognition of a common docking motif (CD) by its activators, substrates, and inactivators.We studied the role of the CD domain of Arabidopsis MPK4 by performing interaction studies and determining the ligand‐bound MPK4 crystal structure.We revealed that the CD domain of MPK4 is essential for interaction and activation by its upstream MAPKKs MKK1, MKK2, and MKK6. Cys181 in the CD site of MPK4 was shown to become sulfenylated in response to reactive oxygen species in vitro. To test the function of C181 in vivo, we generated wild‐type (WT) MPK4‐C181, nonsulfenylatable MPK4‐C181S, and potentially sulfenylation mimicking MPK4‐C181D lines in the mpk4 knockout background. We analyzed the phenotypes in growth, development, and stress responses, revealing that MPK4‐C181S has WT activity and complements the mpk4 phenotype. By contrast, MPK4‐C181D cannot be activated by upstream MAPKK and cannot complement the phenotypes of mpk4.Our findings show that the CD motif is essential and is required for activation by upstream MAPKK for MPK4 function. Furthermore, growth, development, or immunity functions require upstream activation of the MPK4 protein kinase. [ABSTRACT FROM AUTHOR]

SUMMARY: The enzyme DWARF27 (D27) catalyzes the reversible isomerization of all‐trans‐ into 9‐cis‐β‐carotene, initiating strigolactone (SL) biosynthesis. Genomes of higher plants encode two D27‐homologs, D27‐like1 and ‐like2, with unknown functions. Here, we investigated the enzymatic activity and biological function of the Arabidopsis D27‐like1. In vitro enzymatic assays and expression in Synechocystis sp. PCC6803 revealed an unreported 13‐cis/15‐cis/9‐cis‐ and a 9‐cis/all‐trans‐β‐carotene isomerization. Although disruption of AtD27‐like1 did not cause SL deficiency phenotypes, overexpression of AtD27‐like1 in the d27 mutant restored the more‐branching phenotype, indicating a contribution of AtD27‐like1 to SL biosynthesis. Accordingly, generated d27 d27like1 double mutants showed a more pronounced branching phenotype compared to d27. The contribution of AtD27‐like1 to SL biosynthesis is likely a result of its formation of 9‐cis‐β‐carotene that was present at higher levels in AtD27‐like1 overexpressing lines. By contrast, AtD27‐like1 expression correlated negatively with the content of 9‐cis‐violaxanthin, a precursor of ABA, in shoots. Consistently, ABA levels were higher in shoots and also in dry seeds of the d27like1 and d27 d27like1 mutants. Transgenic lines expressing GUS driven by the AtD27LIKE1 promoter and transcript analysis of hormone‐treated Arabidopsis seedlings revealed that AtD27LIKE1 is expressed in different tissues and affects ABA and auxin. Taken together, our work reports a cis/cis‐β‐carotene isomerase that affects the content of both cis‐carotenoid‐derived plant hormones, ABA and SLs. Significance Statement: AtD27LIKE1 is involved in the biosynthesis of the two carotenoid‐derived plant hormones ABA and strigolactones (SLs), by feeding SL biosynthesis at the same time as negatively impacting ABA content. [ABSTRACT FROM AUTHOR]

Jasmine [Jasminum sambac (L.) Aiton] is a commercially important cultivated plant species known for its fragrant flowers used in the perfume industry, medicine and cosmetics. In the present study, we obtained a draft genome for the J. sambac cultivar 'Danbanmoli' (JSDB, a single-petal phenotype). We showed that the final genome of J. sambac was 520.80 Mb in size (contig N50 = 145.43 kb; scaffold N50 = 145.53 kb) and comprised 35,363 genes. Our analyses revealed that the J. sambac genome has undergone only an ancient whole-genome duplication (WGD) event. We estimated that the lineage that has given rise to J. sambac diverged from the lineage leading to Osmanthus fragrans and Olea europaea approximately 31.1 million years ago (Mya). On the basis of a combination of genomic and transcriptomic analyses, we identified 92 transcription factors (TFs) and 206 genes related to heat stress response. Base on a combination of genomic, transcriptomic and metabolomic analyses, a range of aroma compounds and genes involved in the benzenoid/ phenylpropanoid and terpenoid biosynthesis pathways were identified. In the newly assembled J. sambac genome, we identified a total of 122 MYB, 122 bHLH and 69 WRKY genes. Our assembled J. sambac JSDB genome provides fundamental knowledge to study the molecular mechanism of heat stress tolerance, and improve jasmine flowers and dissect its fragrance. [ABSTRACT FROM AUTHOR]

In a multicellular organism, normal growth requires control of cell division to generate cells that are similar to or different from their parents. Analysis of this process in plant roots reveals how this mechanism is regulated.What governs which of two types of cell division occurs in plants. [ABSTRACT FROM AUTHOR]

Global food security is a critical concern that needs practical solutions to feed the expanding human population. A promising approach is the employment of biostimulants to increase crop production. Biostimulants include compounds that boost plant growth. Recently, mimics of zaxinone (MiZax) were shown to have a promising growth-promoting effect in rice (Oryza sativa). In this study, we investigated the effect of MiZax on the growth and yield of three dicot horticultural plants, namely, tomato (Solanum lycopersicum), capsicum (Capsicum annuum), and squash (Cucurbita pepo) in different growth environments, as well as on the growth and development of the monocot date palm (Phoenix dactylifera), an important crop in the Middle East. The application of MiZax significantly enhanced plant height, flower, and branch numbers, fruit size, and total fruit yield in independent field trials from 2020 to 2021. Importantly, the amount of applied MiZax was far less than that used with the commercial compound humic acid, a widely used biostimulant in horticulture. Our results indicate that MiZax have significant application potential to improve the performance and productivity of horticultural crops. [ABSTRACT FROM AUTHOR]

Author(s): Yuchen Long [1, 2]; Yvonne Stahl [3]; Stefanie Weidtkamp-Peters [4]; Marten Postma [5]; Wenkun Zhou [1]; Joachim Goedhart [5]; Mara-Isabel Snchez-Prez [6]; Theodorus W. J. Gadella [5]; Rdiger Simon [...]

Precision farming has the potential to increase global food production capacity whilst minimizing traditional inputs. However, the adoption and impact of precision farming are contingent on the availability of sensors that can discern the state of crops, while not interfering with their growth. Electrical impedance spectroscopy offers an avenue for nondestructive monitoring of crops. To that end, it is reported on the deployment of impedimetric sensors utilizing microneedles (MNs) that can be used to pierce the waxy exterior of plants to obtain sensitive impedance spectra in open‐air settings with an average relative noise value of 3.83%. The sensors are fabricated using a novel micromolding and release method that is compatible with UV photocurable and thermosetting polymers. Assessments of the quality of the MNs under scanning electron microscopy show that the replication process is high in fidelity to the original design of the master mold and that it can be used for upward of 20 replication cycles. The sensor's performance is validated against conventional planar sensors for obtaining the impedance values of Arabidopsis thaliana. As a change is detected in impedance due to lighting and hydration, this raises the possibility for their widespread use in precision farming. [ABSTRACT FROM AUTHOR]

Summary: Carotenoid‐derived regulatory metabolites and hormones are generally known to arise through the oxidative cleavage of a single double bond in the carotenoid backbone, which yields mono‐carbonyl products called apocarotenoids. However, the extended conjugated double bond system of these pigments predestines them also to repeated cleavage forming dialdehyde products, diapocarotenoids, which have been less investigated due to their instability and low abundance. Recently, we reported on the short diapocarotenoid anchorene as an endogenous Arabidopsis metabolite and specific signaling molecule that promotes anchor root formation. In this work, we investigated the biological activity of a synthetic isomer of anchorene, iso‐anchorene, which can be derived from repeated carotenoid cleavage. We show that iso‐anchorene is a growth inhibitor that specifically inhibits primary root growth by reducing cell division rates in the root apical meristem. Using auxin efflux transporter marker lines, we also show that the effect of iso‐anchorene on primary root growth involves the modulation of auxin homeostasis. Moreover, by using liquid chromatography–mass spectrometry analysis, we demonstrate that iso‐anchorene is a natural Arabidopsis metabolite. Chemical inhibition of carotenoid biosynthesis led to a significant decrease in the iso‐anchorene level, indicating that it originates from this metabolic pathway. Taken together, our results reveal a novel carotenoid‐derived regulatory metabolite with a specific biological function that affects root growth, manifesting the biological importance of diapocarotenoids. [ABSTRACT FROM AUTHOR]

INDETERMINATE DOMAIN (IDD)/ BIRD proteins are a highly conserved plant-specific family of transcription factors which play multiple roles in plant development and physiology. Here, we show that mutation in IDD4/IMPERIAL EAGLE increases resistance to the hemi-biotrophic pathogen Pseudomonas syringae, indicating that IDD4 may act as a repressor of basal immune response and PAMP-triggered immunity. Furthermore, the idd4 mutant exhibits enhanced plant-growth indicating IDD4 as suppressor of growth and development. Transcriptome comparison of idd4 mutants and IDD4ox lines aligned to genome-wide IDD4 DNA-binding studies revealed major target genes related to defense and developmental-biological processes. IDD4 is a phospho-protein that interacts and becomes phosphorylated on two conserved sites by the MAP kinase MPK6. DNA-binding studies of IDD4 after flg22 treatment and with IDD4 phosphosite mutants show enhanced binding affinity to ID1 motif-containing promoters and its function as a transcriptional regulator. In contrast to the IDD4-phospho-dead mutant, the IDD4 phospho-mimicking mutant shows altered susceptibility to PstDC3000, salicylic acid levels and transcriptome reprogramming. In summary, we found that IDD4 regulates various hormonal pathways thereby coordinating growth and development with basal immunity. [ABSTRACT FROM AUTHOR]

Protein complex formation has been extensively studied using Förster resonance energy transfer (FRET) measured by Fluorescence Lifetime Imaging Microscopy (FLIM). However, implementing this technology to detect protein interactions in living multicellular organism at single-cell resolution and under native condition is still difficult to achieve. Here we describe the optimization of the labeling conditions to detect FRET-FLIM in living plants. This study exemplifies optimization procedure involving the identification of the optimal position for the labels either at the N or C terminal region and the selection of the bright and suitable, fluorescent proteins as donor and acceptor labels for the FRET study. With an effective optimization strategy, we were able to detect the interaction between the stem cell regulators SHORT-ROOT and SCARECROW at endogenous expression levels in the root pole of living Arabidopsis embryos and developing lateral roots by FRET-FLIM. Using this approach we show that the spatial profile of interaction between two transcription factors can be highlymodulated in reoccurring and structurally resembling organs, thus providing new information on the dynamic redistribution of nuclear protein complex configurations in different developmental stages. In principle, our optimization procedure for transcription factor complexes is applicable to any biological system. [ABSTRACT FROM AUTHOR]

Plant morphogenesis is strongly dependent on the directional growth and the subsequent oriented division of individual cells. It has been shown that the plant cortical microtubule array plays a key role in controlling both these processes. This ordered structure emerges as the collective result of stochastic interactions between large numbers of dynamic microtubules. To elucidate this complex self-organization process a number of analytical and computational approaches to study the dynamics of cortical microtubules have been proposed. To date, however, these models have been restricted to two dimensional planes or geometrically simple surfaces in three dimensions, which strongly limits their applicability as plant cells display a wide variety of shapes. This limitation is even more acute, as both local as well as global geometrical features of cells are expected to influence the overall organization of the array. Here we describe a framework for efficiently simulating microtubule dynamics on triangulated approximations of arbitrary three dimensional surfaces. This allows the study of microtubule array organization on realistic cell surfaces obtained by segmentation of microscopic images. We validate the framework against expected or known results for the spherical and cubical geometry. We then use it to systematically study the individual contributions of global geometry, cell-edge induced catastrophes and cell-face induced stability to array organization in a cuboidal geometry. Finally, we apply our framework to analyze the highly non-trivial geometry of leaf pavement cells of Arabidopsis thaliana, Nicotiana benthamiana and Hedera helix. We show that our simulations can predict multiple features of the microtubule array structure in these cells, revealing, among others, strong constraints on the orientation of division planes. [ABSTRACT FROM AUTHOR]

During multicellular development, specification of distinct cell fates is often regulated by the same transcription factors operating differently in distinct cis-regulatory modules, either through different protein complexes, conformational modification of protein complexes, or combinations of both. Direct visualization of different transcription factor complex states guiding specific gene expression programs has been challenging. Here we use in vivo FRET-FLIM (Förster resonance energy transfer measured by fluorescence lifetime microscopy) to reveal spatial partitioning of protein interactions in relation to specification of cell fate. We show that, in Arabidopsis roots, three fully functional fluorescently tagged cell fate regulators establish cell-type-specific interactions at endogenous expression levels and can form higher order complexes. We reveal that cell-type-specific in vivo FRET-FLIM distributions reflect conformational changes of these complexes to differentially regulate target genes and specify distinct cell fates. [ABSTRACT FROM AUTHOR]

The rapidly proliferating cells in plant meristems must be protected from genome damage. Here, we show that the regulatory role of the Arabidopsis RETINOBLASTOMA RELATED ( RBR) in cell proliferation can be separated from a novel function in safeguarding genome integrity. Upon DNA damage, RBR and its binding partner E2 FA are recruited to heterochromatic γH2 AX-labelled DNA damage foci in an ATM- and ATR-dependent manner. These γH2 AX-labelled DNA lesions are more dispersedly occupied by the conserved repair protein, At BRCA1, which can also co-localise with RBR foci. RBR and At BRCA1 physically interact in vitro and in planta. Genetic interaction between the RBR-silenced ami RBR and Atbrca1 mutants suggests that RBR and At BRCA1 may function together in maintaining genome integrity. Together with E2 FA, RBR is directly involved in the transcriptional DNA damage response as well as in the cell death pathway that is independent of SOG1, the plant functional analogue of p53. Thus, plant homologs and analogues of major mammalian tumour suppressor proteins form a regulatory network that coordinates cell proliferation with cell and genome integrity. [ABSTRACT FROM AUTHOR]

Therootmeristem(RM) isafundamental structure that is responsible for postembryonic root growth.TheRMcontainsthequiescent center(QC), stemcells and frequently dividingmeristematic cells, inwhich the timing and the frequency of cell division are tightly regulated. In Arabidopsis thaliana, several gain-of-function analyses have demonstrated that peptide ligands of the CLAVATA3 (CLV3)/EMBRYO SURROUNDING REGION-RELATED (CLE) family are important for maintaining RM size. Here, we demonstrate that a plant U-box E3 ubiquitin ligase, PUB4, is a novel downstreamcomponent of CLV3/CLE signaling in the RM. Mutations in PUB4 reduced the inhibitory effect of exogenous CLV3/CLE peptide on root cell proliferation and columella stem cell maintenance. Moreover, pub4 mutants grown without exogenous CLV3/CLE peptide exhibited characteristic phenotypes in the RM, such as enhanced root growth, increased number of cortex/endodermis stem cells and decreased number of columella layers. Our phenotypic and gene expression analyses indicated that PUB4 promotes expression of a cell cycle regulatory gene, CYCD6;1, and regulates formative periclinal asymmetric cell divisions in endodermis and cortex/ endodermis initial daughters. These data suggest that PUB4 functions asa global regulator of cell proliferation and the timingof asymmetric cell division that are important for final root architecture. [ABSTRACT FROM AUTHOR]

Plants, as sessile organisms, have evolved a remarkable developmental plasticity to cope with their changing environment. When growing in hostile desert conditions, plants have to grow and thrive in heat and drought. This review discusses how desert plants have adapted their root system architecture (RSA) to cope with scarce water availability and poor nutrient availability in the desert soil. First, we describe how some species can survive by developing deep tap roots to access the groundwater while others produce shallow roots to exploit the short rain seasons and unpredictable rainfalls. Then, we discuss how desert plants have evolved unique developmental programs like having determinate meristems in the case of cacti while forming a branched and compact root system that allows efficient water uptake during wet periods. The remote germination mechanism in date palms is another example of developmental adaptation to survive in the dry and hot desert surface. Date palms have also designed non-gravitropic secondary roots, termed pneumatophores, to maximize water and nutrient uptake. Next, we highlight the distinct anatomical features developed by desert species in response to drought like narrow vessels, high tissue suberization, and air spaces within the root cortex tissue. Finally, we discuss the beneficial impact of the microbiome in promoting root growth in desert conditions and how these characteristics can be exploited to engineer resilient crops with a greater ability to deal with salinity induced by irrigation and with the increasing drought caused by global warming. [ABSTRACT FROM AUTHOR]

Ferns are a representative clade in plant evolution although underestimated in the genomic era. Ceratopteris richardii is an emergent model for developmental processes in ferns, yet a complete scheme of the different growth stages is necessary. Here, we present a developmental analysis, at the tissue and cellular levels, of the first shoot-borne root of Ceratopteris. We followed early stages and emergence of the root meristem in sporelings. While assessing root growth, the first shoot-borne root ceases its elongation between the emergence of the fifth and sixth roots, suggesting Ceratopteris roots follow a determinate developmental program. We report cell division frequencies in the stem cell niche after detecting labeled nuclei in the root apical cell (RAC) and derivatives after 8 h of exposure. These results demonstrate the RAC has a continuous mitotic activity during root development. Detection of cell cycle activity in the RAC at early times suggests this cell acts as a non-quiescent organizing center. Overall, our results provide a framework to study root function and development in ferns and to better understand the evolutionary history of this organ. [ABSTRACT FROM AUTHOR]

Plants are sessile and have to cope with environmentally induced damage through modification of growth and defense pathways. How tissue regeneration is triggered in such responses and whether this involves stem cell activation is an open question. The stress hormone jasmonate (JA) plays well-established roles in wounding and defense responses. JA also affects growth, which is hitherto interpreted as a trade-off between growth and defense. Here, we describe a molecular network triggered by wound-induced JA that promotes stem cell activation and regeneration. JA regulates organizer cell activity in the root stem cell niche through the RBR-SCR network and stress response protein ERF115. Moreover, JA-induced ERF109 transcription stimulates CYCD6;1 expression, functions upstream of ERF115, and promotes regeneration. Soil penetration and response to nematode herbivory induce and require this JA-mediated regeneration response. Therefore, the JA tissue damage response pathway induces stem cell activation and regeneration and activates growth after environmental stress. • The plant RETINOBLASTOMA homolog integrates wound signaling pathways • Jasmonate signaling promotes tissue regeneration • Synergy between jasmonate and auxin signaling in regulating regeneration • Jasmonate-mediated regeneration response is required for abiotic and biotic stresses Stem cell activation and regeneration after tissue damage in Arabidopsis roots is mediated by a jasmonate signaling network. [ABSTRACT FROM AUTHOR]