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The group of voltage-independent K+ channels in Arabidopsis thaliana consists of six members, five tandem-pore channels (TPK1–TPK5) and a single Kir-like channel (KCO3). All TPK/KCO channels are located at the vacuolar membrane except for TPK4, which was shown to be a plasma membrane channel in pollen. The vacuolar channels interact with 14-3-3 proteins (also called General Regulating Factors, GRFs), indicating regulation at the level of protein–protein interactions. Here we review current knowledge about these ion channels and their genes, and highlight open questions that need to be urgently addressed in future studies to fully appreciate the physiological functions of these ion channels. [ABSTRACT FROM AUTHOR]

Leaf senescence is a developmentally regulated process that contributes to nutrient redistribution during reproductive growth and finally leads to tissue death. Manipulating leaf senescence through breeding or genetic engineering may help to improve important agronomic traits, such as crop yield and the storage life of harvested organs. Here, we studied natural variations in the regulation of plant senescence among 16 Arabidopsis thaliana accessions. Chlorophyll content and the proportion of yellow leaves were used as indicator parameters to determine leaf and plant senescence respectively. Our study indicated significant genotype effects on the onset and development of senescence. We selected three late- and five early-senescence accessions for further physiological studies. The relationship between leaf and plant senescence was accession-dependent. There was a significant correlation between plant senescence and the total number of leaves, siliques and plant bolting age. We monitored expression of two senescence marker genes, SAG12 and WRKY53, to evaluate progression of senescence. Our data revealed that chlorophyll content does not fully reflect leaf age, because even fully green leaves had already commenced senescence at the molecular level. Integrating senescence parameters, such as the proportion of senescent leaves, at the whole plant level provided a better indication of the molecular status of the plant than single leaf senescence parameters. [ABSTRACT FROM AUTHOR]

The Arabidopsis tandem-pore K+ (TPK) channels displaying four transmembrane domains and two pore regions share structural homologies with their animal counterparts of the KCNK family. In contrast to the Shaker-like Arabidopsis channels (six transmembrane domains/one pore region), the functional properties and the biological role of plant TPK channels have not been elucidated yet Here, we show that AtTPK4 (KCO4) localizes to the plasma membrane and is predominantly expressed in pollen. AtTPK4 (KCO4) resembles the electrical properties of a voltage-independent K+ channel after expression in Xenopus oocytes and yeast. Hyperpolarizing as well as depolarizing membrane voltages elicited instantaneous K+ currents, which were blocked by extracellular calcium and cytoplasmic protons. Functional complementation assays using a K+ transport-deficient yeast confirmed the biophysical and pharmacological properties of the AtTPK4 channel. The features of AtTPK4 point toward a role in potassium homeostasis and membrane voltage control of the growing pollen tube. Thus, AtTPK4 represents a member of plant tandem-pore-K+ channels, resembling the characteristics of its animal counterparts as well as plant-specific features with respect to modulation of channel activity by acidosis and calcium. [ABSTRACT FROM AUTHOR]

Abstract Background Leishmania tarentolae, a unicellular eukaryotic protozoan, has been established as a novel host for recombinant protein production in recent years. Current protocols for protein expression in Leishmania are, however, time consuming and require extensive lab work in order to identify well-expressing cell lines. Here we established an alternative protein expression work-flow that employs recently engineered infrared fluorescence protein (IFP) as a suitable and easy-to-handle reporter protein for recombinant protein expression in Leishmania. As model proteins we tested three proteins from the plant Arabidopsis thaliana, including a NAC and a type-B ARR transcription factor. Results IFP and IFP fusion proteins were expressed in Leishmania and rapidly detected in cells by deconvolution microscopy and in culture by infrared imaging of 96-well microtiter plates using small cell culture volumes (2 μL - 100 μL). Motility, shape and growth of Leishmania cells were not impaired by intracellular accumulation of IFP. In-cell detection of IFP and IFP fusion proteins was straightforward already at the beginning of the expression pipeline and thus allowed early pre-selection of well-expressing Leishmania clones. Furthermore, IFP fusion proteins retained infrared fluorescence after electrophoresis in denaturing SDS-polyacrylamide gels, allowing direct in-gel detection without the need to disassemble cast protein gels. Thus, parameters for scaling up protein production and streamlining purification routes can be easily optimized when employing IFP as reporter. Conclusions Using IFP as biosensor we devised a protocol for rapid and convenient protein expression in Leishmania tarentolae. Our expression pipeline is superior to previously established methods in that it significantly reduces the hands-on-time and work load required for identifying well-expressing clones, refining protein production parameters and establishing purification protocols. The facile in-cell and in-gel detection tools built on IFP make Leishmania amenable for high-throughput expression of proteins from plant and animal sources.

Abstract Background Medium- to large-scale expression profiling using quantitative polymerase chain reaction (qPCR) assays are becoming increasingly important in genomics research. A major bottleneck in experiment preparation is the design of specific primer pairs, where researchers have to make several informed choices, often outside their area of expertise. Using currently available primer design tools, several interactive decisions have to be made, resulting in lengthy design processes with varying qualities of the assays. Results Here we present QuantPrime, an intuitive and user-friendly, fully automated tool for primer pair design in small- to large-scale qPCR analyses. QuantPrime can be used online through the internet http://www.quantprime.de/ or on a local computer after download; it offers design and specificity checking with highly customizable parameters and is ready to use with many publicly available transcriptomes of important higher eukaryotic model organisms and plant crops (currently 295 species in total), while benefiting from exon-intron border and alternative splice variant information in available genome annotations. Experimental results with the model plant Arabidopsis thaliana, the crop Hordeum vulgare and the model green alga Chlamydomonas reinhardtii show success rates of designed primer pairs exceeding 96%. Conclusion QuantPrime constitutes a flexible, fully automated web application for reliable primer design for use in larger qPCR experiments, as proven by experimental data. The flexible framework is also open for simple use in other quantification applications, such as hydrolyzation probe design for qPCR and oligonucleotide probe design for quantitative in situ hybridization. Future suggestions made by users can be easily implemented, thus allowing QuantPrime to be developed into a broad-range platform for the design of RNA expression assays.

Abstract Background In plants, complex regulatory mechanisms are at the core of physiological and developmental processes. The phytohormone abscisic acid (ABA) is involved in the regulation of various such processes, including stomatal closure, seed and bud dormancy, and physiological responses to cold, drought and salinity stress. The underlying tissue or plant-wide control circuits often include combinatorial gene regulatory mechanisms and networks that we are only beginning to unravel with the help of new molecular tools. The increasing availability of genomic sequences and gene expression data enables us to dissect ABA regulatory mechanisms at the individual gene expression level. In this paper we used an in-silico-based approach directed towards genome-wide prediction and identification of specific features of ABA-responsive elements. In particular we analysed the genome-wide occurrence and positional arrangements of two well-described ABA-responsive cis-regulatory elements (CREs), ABRE and CE3, in thale cress (Arabidopsis thaliana) and rice (Oryza sativa). Results Our results show that Arabidopsis and rice use the ABA-responsive elements ABRE and CE3 distinctively. Earlier reports for various monocots have identified CE3 as a coupling element (CE) associated with ABRE. Surprisingly, we found that while ABRE is equally abundant in both species, CE3 is practically absent in Arabidopsis. ABRE-ABRE pairs are common in both genomes, suggesting that these can form functional ABA-responsive complexes (ABRCs) in Arabidopsis and rice. Furthermore, we detected distinct combinations, orientation patterns and DNA strand preferences of ABRE and CE3 motifs in rice gene promoters. Conclusion Our computational analyses revealed distinct recruitment patterns of ABA-responsive CREs in upstream sequences of Arabidopsis and rice. The apparent absence of CE3s in Arabidopsis suggests that another CE pairs with ABRE to establish a functional ABRC capable of interacting with transcription factors. Further studies will be needed to test whether the observed differences are extrapolatable to monocots and dicots in general, and to understand how they contribute to the fine-tuning of the hormonal response. The outcome of our investigation can now be used to direct future experimentation designed to further dissect the ABA-dependent regulatory networks.

Abstract Background Quantitative reverse transcription – polymerase chain reaction (qRT-PCR) has been demonstrated to be particularly suitable for the analysis of weakly expressed genes, such as those encoding transcription factors. Rice (Oryza sativa L.) is an important crop and the most advanced model for monocotyledonous species; its nuclear genome has been sequenced and molecular tools are being developed for functional analyses. However, high-throughput methods for rice research are still limited and a large-scale qRT-PCR platform for gene expression analyses has not been reported. Results We established a qRT-PCR platform enabling the multi-parallel determination of the expression levels of more than 2500 rice transcription factor genes. Additionally, using different rice cultivars, tissues and physiological conditions, we evaluated the expression stability of seven reference genes. We demonstrate this resource allows specific and reliable detection of the expression of transcription factor genes in rice. Conclusion Multi-parallel qRT-PCR allows the versatile and sensitive transcriptome profiling of large numbers of rice transcription factor genes. The new platform complements existing microarray-based expression profiling techniques, by allowing the analysis of lowly expressed transcription factor genes to determine their involvement in developmental or physiological processes. We expect that this resource will be of broad utility to the scientific community in the further development of rice as an important model for plant science.

Abstract Background Transcription factors (TFs) are key regulatory proteins that enhance or repress the transcriptional rate of their target genes by binding to specific promoter regions (i.e. cis-acting elements) upon activation or de-activation of upstream signaling cascades. TFs thus constitute master control elements of dynamic transcriptional networks. TFs have fundamental roles in almost all biological processes (development, growth and response to environmental factors) and it is assumed that they play immensely important functions in the evolution of species. In plants, TFs have been employed to manipulate various types of metabolic, developmental and stress response pathways. Cross-species comparison and identification of regulatory modules and hence TFs is thought to become increasingly important for the rational design of new plant biomass. Up to now, however, no computational repository is available that provides access to the largely complete sets of transcription factors of sequenced plant genomes. Description PlnTFDB is an integrative plant transcription factor database that provides a web interface to access large (close to complete) sets of transcription factors of several plant species, currently encompassing Arabidopsis thaliana (thale cress), Populus trichocarpa (poplar), Oryza sativa (rice), Chlamydomonas reinhardtii and Ostreococcus tauri. It also provides an access point to its daughter databases of a species-centered representation of transcription factors (OstreoTFDB, ChlamyTFDB, ArabTFDB, PoplarTFDB and RiceTFDB). Information including protein sequences, coding regions, genomic sequences, expressed sequence tags (ESTs), domain architecture and scientific literature is provided for each family. Conclusion We have created lists of putatively complete sets of transcription factors and other transcriptional regulators for five plant genomes. They are publicly available through http://plntfdb.bio.uni-potsdam.de. Further data will be included in the future when the sequences of other plant genomes become available.

Quinoa (Chenopodium quinoa Willd.), an Andean crop, is a facultative halophyte food crop recognized globally for its high nutritional value and plasticity to adapt to harsh conditions. We conducted a genome-wide association study on a diverse set of quinoa germplasm accessions. These accessions were evaluated for the following agronomic and biochemical traits: days to 50% flowering (DTF), plant height (PH), panicle length (PL), stem diameter (SD), seed yield (SY), grain diameter (GD), and thousand-grain weight (TGW). These accessions underwent genotyping-by-sequencing using the DNBSeq-G400R platform. Among all evaluated traits, TGW represented maximum broad-sense heritability. Our study revealed average SNP density of ≈ 3.11 SNPs/10 kb for the whole genome, with the lowest and highest on chromosomes Cq1B and Cq9A, respectively. Principal component analysis clustered the quinoa population in three main clusters, one clearly representing lowland Chilean accessions, whereas the other two groups corresponded to germplasm from the highlands of Peru and Bolivia. In our germplasm set, we estimated linkage disequilibrium decay to be ≈ 118.5 kb. Marker-trait analyses revealed major and consistent effect associations for DTF on chromosomes 3A, 4B, 5B, 6A, 7A, 7B and 8B, with phenotypic variance explained (PVE) as high as 19.15%. Nine associations across eight chromosomes were also found for saponin content with 20% PVE by qSPN5A.1. More QTLs were identified for PL and TGW on multiple chromosomal locations. We identified putative candidate genes in the genomic regions associated with DTF and saponin content. The consistent and major-effect genomic associations can be used in fast-tracking quinoa breeding for wider adaptation across marginal environments., (© 2024. The Author(s).)

The shoot apical meristem (SAM) is responsible for overall shoot growth by generating all aboveground structures. Recent research has revealed that the SAM displays an autonomous heat stress (HS) memory of a previous non-lethal HS event. Considering the importance of the SAM for plant growth, it is essential to determine how its thermomemory is mechanistically controlled. Here, we report that HEAT SHOCK TRANSCRIPTION FACTOR A7b (HSFA7b) plays a crucial role in this process in Arabidopsis, as the absence of functional HSFA7b results in the temporal suppression of SAM activity after thermopriming. We found that HSFA7b directly regulates ethylene response at the SAM by binding to the promoter of the key ethylene signaling gene ETHYLENE-INSENSITIVE 3 to establish thermotolerance. Moreover, we demonstrated that HSFA7b regulates the expression of ETHYLENE OVERPRODUCER 1 (ETO1) and ETO1-LIKE 1, both of which encode ethylene biosynthesis repressors, thereby ensuring ethylene homeostasis at the SAM. Taken together, these results reveal a crucial and tissue-specific role for HSFA7b in thermomemory at the Arabidopsis SAM., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Haberlea rhodopensis, a resurrection species, is the only plant known to be able to survive multiple extreme environments, including desiccation, freezing temperatures, and long-term darkness. However, the molecular mechanisms underlying tolerance to these stresses are poorly studied. Here, we present a high-quality genome of Haberlea and found that ~ 23.55% of the 44,306 genes are orphan. Comparative genomics analysis identified 89 significantly expanded gene families, of which 25 were specific to Haberlea. Moreover, we demonstrated that Haberlea preserves its resurrection potential even in prolonged complete darkness. Transcriptome profiling of plants subjected to desiccation, darkness, and low temperatures revealed both common and specific footprints of these stresses, and their combinations. For example, PROTEIN PHOSPHATASE 2C (PP2C) genes were substantially induced in all stress combinations, while PHYTOCHROME INTERACTING FACTOR 1 (PIF1) and GROWTH RESPONSE FACTOR 4 (GRF4) were induced only in darkness. Additionally, 733 genes with unknown functions and three genes encoding transcription factors specific to Haberlea were specifically induced/repressed upon combination of stresses, rendering them attractive targets for future functional studies. The study provides a comprehensive understanding of the genomic architecture and reports details of the mechanisms of multi-stress tolerance of this resurrection species that will aid in developing strategies that allow crops to survive extreme and multiple abiotic stresses., (© 2024. The Author(s).)

Senescence is a highly regulated process driven by developmental age and environmental factors. Although leaf senescence is accelerated by nitrogen (N) deficiency, the underlying physiological and molecular mechanisms are largely unknown. Here, we reveal that BBX14, a previously uncharacterized BBX-type transcription factor in Arabidopsis, is crucial for N starvation-induced leaf senescence. We find that inhibiting BBX14 by artificial miRNA (amiRNA) accelerates senescence during N starvation and in darkness, while BBX14 overexpression (BBX14-OX) delays it, identifying BBX14 as a negative regulator of N starvation- and dark-induced senescence. During N starvation, nitrate and amino acids like glutamic acid, glutamine, aspartic acid, and asparagine were highly retained in BBX14-OX leaves compared to the wild type. Transcriptome analysis showed a large number of senescence-associated genes (SAGs) to be differentially expressed between BBX14-OX and wild-type plants, including ETHYLENE INSENSITIVE3 (EIN3) which regulates N signaling and leaf senescence. Chromatin immunoprecipitation (ChIP) showed that BBX14 directly regulates EIN3 transcription. Furthermore, we revealed the upstream transcriptional cascade of BBX14. By yeast one-hybrid screen and ChIP, we found that MYB44, a stress-responsive MYB transcription factor, directly binds to the promoter of BBX14 and activates its expression. In addition, Phytochrome Interacting Factor 4 (PIF4) binds to the promoter of BBX14 to repress BBX14 transcription. Thus, BBX14 functions as a negative regulator of N starvation-induced senescence through EIN3 and is directly regulated by PIF4 and MYB44., (© 2023 The Authors. The Plant Journal published by Society for Experimental Biology and John Wiley & Sons Ltd.)

Vascular plants display a huge variety of longevity patterns, from a few weeks for several annual species up to thousands of years for some perennial species. Understanding how longevity variation is structured has long been considered a fundamental aspect of the life sciences in view of evolution, species distribution, and adaptation to diverse environments. Unlike animals, whose organs are typically formed during embryogenesis, vascular plants manage to extend their life by continuously producing new tissues and organs in apical and lateral directions via proliferation of stem cells located within specialized tissues called meristems. Stem cells are the main source of plant longevity. Variation in plant longevity is highly dependent on the activity and fate identity of stem cells. Multiple developmental factors determine how stem cells contribute to variation in plant longevity. In this review, we provide an overview of the genetic mechanisms, hormonal signaling, and environmental factors involved in controlling plant longevity through long-term maintenance of stem cell fate identity., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

The environment is seldom optimal for plant growth and changes in abiotic and biotic signals, including temperature, water availability, radiation and pests, induce plant responses to optimise survival. The New Zealand native plant species and close relative to Arabidopsis thaliana , Pachycladon cheesemanii, grows under environmental conditions that are unsustainable for many plant species. Here, we compare the responses of both species to different stressors (low temperature, salt and UV-B radiation) to help understand how P. cheesemanii can grow in such harsh environments. The stress transcriptomes were determined and comparative transcriptome and network analyses discovered similar and unique responses within species, and between the two plant species. A number of widely studied plant stress processes were highly conserved in A. thaliana and P. cheesemanii . However, in response to cold stress, Gene Ontology terms related to glycosinolate metabolism were only enriched in P. cheesemanii . Salt stress was associated with alteration of the cuticle and proline biosynthesis in A. thaliana and P. cheesemanii , respectively. Anthocyanin production may be a more important strategy to contribute to the UV-B radiation tolerance in P. cheesemanii . These results allowed us to define broad stress response pathways in A. thaliana and P. cheesemanii and suggested that regulation of glycosinolate, proline and anthocyanin metabolism are strategies that help mitigate environmental stress.

Background: Plant immunity relies on the perception of immunogenic signals by cell-surface and intracellular receptors and subsequent activation of defense responses like programmed cell death. Under certain circumstances, the fine-tuned innate immune system of plants results in the activation of autoimmune responses that cause constitutive defense responses and spontaneous cell death in the absence of pathogens., Results: Here, we characterized the onset of leaf death 12 (old12) mutant that was identified in the Arabidopsis accession Landsberg erecta. The old12 mutant is characterized by a growth defect, spontaneous cell death, plant-defense gene activation, and early senescence. In addition, the old12 phenotype is temperature reversible, thereby exhibiting all characteristics of an autoimmune mutant. Mapping the mutated locus revealed that the old12 phenotype is caused by a mutation in the Lectin Receptor Kinase P2-TYPE PURINERGIC RECEPTOR 2 (P2K2) gene. Interestingly, the P2K2 allele from Landsberg erecta is conserved among Brassicaceae. P2K2 has been implicated in pathogen tolerance and sensing extracellular ATP. The constitutive activation of defense responses in old12 results in improved resistance against Pseudomonas syringae pv. tomato DC3000., Conclusion: We demonstrate that old12 is an auto-immune mutant and that allelic variation of P2K2 contributes to diversity in Arabidopsis immune responses., (© 2023. The Author(s).)

Greenhouse gas (GHG) emissions have created a global climate crisis which requires immediate interventions to mitigate the negative effects on all aspects of life on this planet. As current agriculture and land use contributes up to 25% of total GHG emissions, plant scientists take center stage in finding possible solutions for a transition to sustainable agriculture and land use. In this article, the PlantACT! (Plants for climate ACTion!) initiative of plant scientists lays out a road map of how and in which areas plant scientists can contribute to finding immediate, mid-term, and long-term solutions, and what changes are necessary to implement these solutions at the personal, institutional, and funding levels., Competing Interests: Declaration of interests No interests are declared., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Metabolic engineering approaches do not exclusively require fine-tuning of heterologous genes but oftentimes also modulation or even induction of host gene expression, e.g. , in order to rewire metabolic fluxes. Here, we introduce the programmable red light switch PhiReX 2.0, which can rewire metabolic fluxes by targeting endogenous promoter sequences through single-guide RNAs (sgRNAs) and activate gene expression in Saccharomyces cerevisiae upon red light stimulation. The split transcription factor is built from the plant-derived optical dimer PhyB and PIF3, which is fused to a DNA-binding domain based on the catalytically dead Cas9 protein (dCas9) and a transactivation domain. This design combines at least two major advantages: first, the sgRNAs, guiding dCas9 to the promoter of interest, can be exchanged in an efficient and straightforward Golden Gate-based cloning approach, which allows for rational or randomized combination of up to four sgRNAs in a single expression array. Second, target gene expression can be rapidly upregulated by short red light pulses in a light dose-dependent manner and returned to the native expression level by applying far-red light without interfering with the cell culture. Using the native yeast gene CYC 1 as an example, we demonstrated that PhiReX 2.0 can upregulate CYC 1 gene expression by up to 6-fold in a light intensity-dependent and reversible manner using a single sgRNA.

As a well-recognized traditional Chinese medicine (TCM), immature fruits of Citrus grandis 'Tomentosa' (CGT) serve to cure chronic cough in humans. Specialized metabolites including flavonoids may have contribute to this curing effect. Knowledge about the molecular mechanisms underlying flavonoid biosynthesis in 'Tomentosa' fruits will, therefore, support the breeding of varieties with improved medicinal properties. Hence, we profiled the transcriptomes and metabolites of the fruits of two contrasting C. grandis varieties, namely 'Zheng-Mao' ('ZM') used in TCM production, and a locally cultivated pomelo, namely 'Guang-Qing' ('GQ'), at four developmental stages. A total of 39 flavonoids, including 14 flavanone/flavone, 5 isoflavonoids, 12 flavonols, and 6 anthocyanins, were identified, and 16 of which were quantitatively determined in the fruits of the two varieties. We found that 'ZM' fruits contain more flavonoids than 'GQ'. Specifically, rhoifolin levels were significantly higher in 'ZM' than in 'GQ'. We annotated 31,510 genes, including 1,387 previously unknown ones, via transcriptome sequencing of 'ZM' and 'GQ.' A total of 646 genes were found to be differentially expressed between 'ZM' and 'GQ' throughout at all four fruit developmental stages, indicating that they are robust expression markers for future breeding programs. Weighted gene co-expression network analysis identified 18 modules. Combined transcriptional and metabolic analysis revealed 25 genes related to flavonoid biosynthesis and 16 transcriptional regulators (MYBs, bHLHs, WD40) that may be involved in the flavonoids biosynthesis in C. grandis 'Tomentosa' fruits., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Masson SAS. All rights reserved.)

Autophagy is an evolutionarily conserved degradation pathway in eukaryotes; it plays a critical role in nutritional stress tolerance. The circadian clock is an endogenous timekeeping system that generates biological rhythms to adapt to daily changes in the environment. Accumulating evidence indicates that the circadian clock and autophagy are intimately interwoven in animals. However, the role of the circadian clock in regulating autophagy has been poorly elucidated in plants. Here, we show that autophagy exhibits a robust circadian rhythm in both light/dark cycle (LD) and in constant light (LL) in Arabidopsis. However, autophagy rhythm showed a different pattern with a phase-advance shift and a lower amplitude in LL compared to LD. Moreover, mutation of the transcription factor LUX ARRHYTHMO (LUX) removed autophagy rhythm in LL and led to an enhanced amplitude in LD. LUX represses expression of the core autophagy genes ATG2, ATG8a, and ATG11 by directly binding to their promoters. Phenotypic analysis revealed that LUX is responsible for improved resistance of plants to carbon starvation, which is dependent on moderate autophagy activity. Comprehensive transcriptomic analysis revealed that the autophagy rhythm is ubiquitous in plants. Taken together, our findings demonstrate that the LUX-mediated circadian clock regulates plant autophagy rhythms., (© 2022 The Authors. Journal of Integrative Plant Biology published by John Wiley & Sons Australia, Ltd on behalf of Institute of Botany, Chinese Academy of Sciences.)

Plants 'memorize' stressful events and protect themselves from future, often more severe, stresses. To maximize growth after stress, plants 'reset' or 'forget' memories of stressful situations, which requires an intricate balance between stress memory formation and the degree of forgetfulness. HEAT SHOCK PROTEIN 21 (HSP21) encodes a small heat shock protein in plastids of Arabidopsis thaliana. HSP21 functions as a key component of thermomemory, which requires a sustained elevated level of HSP21 during recovery from heat stress. A heat-induced metalloprotease, filamentation temperature-sensitive H6 (FtsH6), degrades HSP21 to its pre-stress abundance, thereby resetting memory during the recovery phase. The transcription factor heat shock factor A2 (HSFA2) activates downstream genes essential for mounting thermomemory, acting as a positive regulator in the process. Here, using a yeast one-hybrid screen, we identify HSFA2 as an upstream transactivator of the resetting element FtsH6. Constitutive and inducible overexpression of HSFA2 increases expression of FtsH6, whereas it is drastically reduced in the hsfa2 knockout mutant. Chromatin immunoprecipitation reveals in planta binding of HSFA2 to the FtsH6 promoter. Importantly, overexpression of HSFA2 improves thermomemory more profoundly in ftsh6 than wild-type plants. Thus, by activating both memory-supporting and memory-resetting genes, HSFA2 acts as a cellular homeostasis factor during thermomemory., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

Pre-exposing (priming) plants to mild, non-lethal elevated temperature improves their tolerance to a later higher-temperature stress (triggering stimulus), which is of great ecological importance. 'Thermomemory' is maintaining this tolerance for an extended period of time. NAM/ATAF1/2/CUC2 (NAC) proteins are plant-specific transcription factors (TFs) that modulate responses to abiotic stresses, including heat stress (HS). Here, we investigated the potential role of NACs for thermomemory. We determined the expression of 104 Arabidopsis NAC genes after priming and triggering heat stimuli, and found ATAF1 expression is strongly induced right after priming and declines below control levels thereafter during thermorecovery. Knockout mutants of ATAF1 show better thermomemory than wild type, revealing a negative regulatory role. Differential expression analyses of RNA-seq data from ATAF1 overexpressor, ataf1 mutant and wild-type plants after heat priming revealed five genes that might be priming-associated direct targets of ATAF1: AT2G31260 (ATG9), AT2G41640 (GT61), AT3G44990 (XTH31), AT4G27720 and AT3G23540. Based on co-expression analyses applied to the aforementioned RNA-seq profiles, we identified ANAC055 to be transcriptionally co-regulated with ATAF1. Like ataf1, anac055 mutants show improved thermomemory, revealing a potential co-control of both NAC TFs over thermomemory. Our data reveals a core importance of two NAC transcription factors, ATAF1 and ANAC055, for thermomemory., (© 2022. The Author(s).)