The significance of WRKY45 transcription factor in metabolic adjustments during dark-induced leaf senescence

Transcriptome-wide N6-methyladenosinem modifications analysis of growth and fumonisins production in Fusarium proliferatum causing banana crown rot

Crown rot caused by Fusarium proliferatum is a severe postharvest disease of banana fruit. The N6-methyladenosine (m6A) modification is the most common type of RNA modification and regulates gene expression in eukaryotes. Here, we analyzed transcriptome-wide changes in m6A methylation to investigate post-transcriptional regulation mechanisms of growth and fumonisin biosynthesis of F. proliferatum after fluopyram (Flu) treatment. The results demonstrated that Flu treatment inhibited F. proliferatum growth but induced fumonisins (FB1 and FB2) production both in vitro and in vivo. A transcriptome-wide m6A methylation profile showed that m6A hypomethylation was induced by Flu and enriched in start codons and the 3' untranslated region. FpAlkbh8 and FpYthdc1 may contribute to the decrease in m6A modifications after Flu treatment. The expression levels of m6A-containing mRNAs were higher than those of non-m6A-containing mRNAs. Furthermore, Flu decreased the acetyl-CoA content and regulated glycolysis and tricarboxylic acid cycle through m6A modifications, diverting the acetyl-CoA flux into fumonisin biosynthesis. Importantly, Flu-mediated regulation of energy and reactive oxygen species metabolism, cell wall and membrane, and transcription factors was associated with m6A modifications. Collectively, this study provides potential novel targets for improving fungicide efficiency to control fungal disease and highlights the potential of environmental risks of fungicides.

Investigation of the Effectiveness and Molecular Mechanisms of Thiamin Priming to Control Early Blight Disease in Potato

In several plant species, thiamin foliar application primes plant immunity and can be effective in controlling various diseases. However, the effectiveness of thiamin against potato pathogens has seldom been investigated. Additionally, the transcriptomics and metabolomics of immune priming by thiamin have not previously been investigated. Here, we tested the effect of thiamin application against Alternaria solani, the causal agent of early blight in potato, and identified associated changes in gene expression and metabolite content. Thiamin applied on foliage at an optimal concentration of 10 mM reduced lesion size by ∼33%. However, prevention of lesion growth was temporally limited, as a reduction of lesion size occurred when leaves were inoculated 4 h, but not 24 h, following thiamin treatment. Additionally, the effect of thiamin on lesion size was restricted to the application site and was not systemic. RNA-seq analysis showed that thiamin affected the expression of 308 genes involved in the synthesis of salicylic acid, secondary metabolites, fatty acid, chitin, primary metabolism, and photosynthesis. Genes in these pathways were also amongst the thousands of genes differentially regulated in the response to the pathogen alone, though they were often more differentially expressed and enriched when thiamin and the pathogen were combined. Thiamin also delayed the downregulation of photosynthesis-associated genes in plants inoculated with A. solani. Metabolite analyses revealed that thiamin treatment in the absence of a pathogen decreased the amounts of several organic compounds involved in the citric acid cycle. We hypothesize that thiamin primes plant defenses through perturbation of primary metabolism.

Identification and functional characterization of the MYB transcription factor GmMYBLJ in soybean leaf senescence

Leaf senescence is an important agronomic trait that significantly influences the quality and yield of soybeans. v-Myb avian myeloblastosis viral oncogene homolog (MYB) transcription factors are considered crucial regulators governing leaf senescence, which can be utilized to improve agronomic traits in crops. However, our knowledge regarding the functional roles of soybean MYBs in leaf senescence is extremely limited. In this study, GmMYBLJ, a CCA1-like MYB, was identified and functionally characterized with respect to leaf senescence. The GmMYBLJ protein is localized in the nucleus, and a high accumulation of its transcripts was observed in nodules and embryos. Notably, GmMYBLJ was highly expressed in soybean senescent leaves and was transcriptionally induced by dark or NaCl treatment, as confirmed by histochemical GUS staining analysis. Ectopic overexpression of GmMYBLJ in Arabidopsis not only led to earlier leaf senescence, reduced chlorophyll content, and increased MDA accumulation but also promoted the expression of several WRKY family transcription factors and senescence-associated genes, such as SAG12 and ORE1. Further investigation showed that overexpression of GmMYBLJ accelerated Arabidopsis leaf senescence under darkness and in response to Pst DC3000 infection. Moreover, transgenic soybean plants overexpressing GmMYBLJ grew faster and exhibited accelerated senescence under salt stress. DAB staining analysis showed that GmMYBLJ induced ROS accumulation in soybean hairy roots and Arabidopsis leaves. Collectively, our results provided useful information into the functional roles of GmMYBLJ in both age-dependent and stress-induced senescence.

Unravelling the role of WRKY transcription factors in leaf senescence: Genetic and molecular insights

BACKGROUND

Leaf senescence (LS), the final phase in leaf development, is an important and precisely regulated process crucial for plant well-being and the redistribution of nutrients. It is intricately controlled by various regulatory factors, including WRKY transcription factors (TFs). WRKYs are one of the most significant plant TF families, and several of them are differentially regulated and important during LS. Recent research has enhanced our understanding of the structural and functional characteristics of WRKY TFs, providing insights into their regulatory roles.

AIM OF REVIEW

This review aims to elucidate the genetic and molecular mechanisms underlying the intricate regulatory networks associated with LS by investigating the role of WRKY TFs. We seek to highlight the importance of WRKY-mediated signaling pathways in understanding LS, plant evolution, and response to varying environmental conditions.

KEY SCIENTIFIC CONCEPTS OF REVIEW

WRKY TFs exhibit specific DNA-binding activity at the N-terminus and dynamic interactions of the intrinsically disordered domain at the C-terminus with various proteins. These WRKY TFs not only control the activity of other WRKYs, but also interact with either WRKYs or other TFs, thereby fine- tuning the expression of target genes. By unraveling the complex interactions and regulatory mechanisms of WRKY TFs, this review broadens our knowledge of the genetic and molecular basis of LS. Understanding WRKY-mediated signalling pathways provides crucial insights into specific aspects of plant development, such as stress-induced senescence, and offers potential strategies for improving crop resilience to environmental stresses like drought and pathogen attacks. By targeting these pathways, it may be possible to enhance specific productivity traits, such as increased yield stability under adverse conditions, thereby contributing to more reliable agricultural outputs.

How abiotic stresses trigger sugar signaling to modulate leaf senescence?

Plants have evolved the adaptive capacity to mitigate the negative effect of external adversities at chemical, molecular, cellular, and physiological levels. This capacity is conferred by triggering the coordinated action of internal regulatory factors, in which sugars play an essential role in the regulating chloroplast degradation and leaf senescence under various stresses. In this review, we summarize the recent findings on the senescent-associated changes in carbohydrate metabolism and its relation to chlorophyl degradation, oxidative damage, photosynthesis inhibition, programmed cell death (PCD), and sink-source relation as affected by abiotic stresses. The action of sugar signaling in regulating the initiation and progression of leaf senescence under abiotic stresses involves interactions with various plant hormones, reactive oxygen species (ROS) burst, and protein kinases. This discussion aims to elucidate the complex regulatory network and molecular mechanisms that underline sugar-induced leaf senescence in response to various abiotic stresses. The imperative role of sugar signaling in regulating plant stress responses potentially enables the production of crop plants with modified sugar metabolism. This, in turn, may facilitate the engineering of plants with improved stress responses, optimal life span and higher yield achievement.

The interplay between autophagy and chloroplast vesiculation pathways under dark-induced senescence

In cellular circumstances where carbohydrates are scarce, plants can use alternative substrates for cellular energetic maintenance. In plants, the main protein reserve is present in the chloroplast, which contains most of the total leaf proteins and represents a rich source of nitrogen and amino acids. Autophagy plays a key role in chloroplast breakdown, a well-recognised symptom of both natural and stress-induced plant senescence. Remarkably, an autophagic-independent route of chloroplast degradation associated with chloroplast vesiculation (CV) gene was previously demonstrated. During extended darkness, CV is highly induced in the absence of autophagy, contributing to the early senescence phenotype of atg mutants. To further investigate the role of CV under dark-induced senescence conditions, mutants with low expression of CV (amircv) and double mutants amircv1xatg5 were characterised. Following darkness treatment, no aberrant phenotypes were observed in amircv single mutants; however, amircv1xatg5 double mutants displayed early senescence and altered dismantling of chloroplast and membrane structures under these conditions. Metabolic characterisation revealed that the functional lack of both CV and autophagy leads to higher impairment of amino acid release and differential organic acid accumulation during starvation conditions. The data obtained are discussed in the context of the role of CV and autophagy, both in terms of cellular metabolism and the regulation of chloroplast degradation.

Arabidopsis transcription factor WRKY45 confers cadmium tolerance via activating PCS1 and PCS2 expression

Cadmium (Cd) has long been recognized as toxic pollutant to crops worldwide. The biosynthesis of glutathione-dependent phytochelatin (PC) plays crucial roles in the detoxification of Cd in plants. However, its regulatory mechanism remains elusive. Here, we revealed that Arabidopsis transcription factor WRKY45 confers Cd tolerance via promoting the expression of PC synthesis-related genes PCS1 and PCS2, respectively. Firstly, we found that Cd stress induces the transcript levels of WRKY45 and its protein abundance. Accordingly, in contrast to wild type Col-0, the increased sensitivity to Cd is observed in wrky45 mutant, while overexpressing WRKY45 plants are more tolerant to Cd. Secondly, quantitative real-time PCR revealed that the expression of AtPCS1 and AtPCS2 is stimulated in overexpressing WRKY45 plants, but decreased in wrky45 mutant. Thirdly, WRKY45 promotes the expression of PCS1 and PCS2, electrophoresis mobility shift assay analysis uncovered that WRKY45 directly binds to the W-box cis-element of PCS2 promoter. Lastly, the overexpression of WRKY45 in Col-0 leads to more accumulation of PCs in Arabidopsis, and the overexpression of PCS1 or PCS2 in wrky45 mutant plants rescues the phenotypes induced by Cd stress. In conclusion, our results show that AtWRKY45 positively regulates Cd tolerance in Arabidopsis via activating PCS1 and PCS2 expression.

Recent advances in cellular degradation and nuclear control of leaf senescence

Senescence is the final stage of plant growth and development, and is a highly regulated process at the molecular, cellular, and organismal levels. When triggered by age, hormonal, or environmental cues, plants actively adjust their metabolism and gene expression to execute the progression of senescence. Regulation of senescence is vital for the reallocation of nutrients to sink organs, to ensure reproductive success and adaptations to stresses. Identification and characterization of hallmarks of leaf senescence are of great importance for understanding the molecular regulatory mechanisms of plant senescence, and breeding future crops with more desirable senescence traits. Tremendous progress has been made in elucidating the genetic network underpinning the metabolic and cellular changes in leaf senescence. In this review, we focus on three hallmarks of leaf senescence - chlorophyll and chloroplast degradation, loss of proteostasis, and activation of senescence-associated genes (SAGs), and discuss recent findings of the molecular players and the crosstalk of senescence pathways.

A Common Molecular Signature Indicates the Pre-Meristematic State of Plant Calli

In response to different degrees of mechanical injury, certain plant cells re-enter the division cycle to provide cells for tissue replenishment, tissue rejoining, de novo organ formation, and/or wound healing. The intermediate tissue formed by the dividing cells is called a callus. Callus formation can also be induced artificially in vitro by wounding and/or hormone (auxin and cytokinin) treatments. The callus tissue can be maintained in culture, providing starting material for de novo organ or embryo regeneration and thus serving as the basis for many plant biotechnology applications. Due to the biotechnological importance of callus cultures and the scientific interest in the developmental flexibility of somatic plant cells, the initial molecular steps of callus formation have been studied in detail. It was revealed that callus initiation can follow various ways, depending on the organ from which it develops and the inducer, but they converge on a seemingly identical tissue. It is not known, however, if callus is indeed a special tissue with a defined gene expression signature, whether it is a malformed meristem, or a mass of so-called "undifferentiated" cells, as is mostly believed. In this paper, I review the various mechanisms of plant regeneration that may converge on callus initiation. I discuss the role of plant hormones in the detour of callus formation from normal development. Finally, I compare various Arabidopsis gene expression datasets obtained a few days, two weeks, or several years after callus induction and identify 21 genes, including genes of key transcription factors controlling cell division and differentiation in meristematic regions, which were upregulated in all investigated callus samples. I summarize the information available on all 21 genes that point to the pre-meristematic nature of callus tissues underlying their wide regeneration potential.

Autophagy modulates growth and development in the moss Physcomitrium patens

Physcomitrium patens apical growing protonemal cells have the singularity that they continue to undergo cell divisions as the plant develops. This feature provides a valuable tool to study autophagy in the context of a multicellular apical growing tissue coupled to development. Herein, we showed that the core autophagy machinery is present in the moss P. patens, and characterized the 2D and 3D growth and development of atg5 and atg7 loss-of-function mutants under optimal and nutrient-deprived conditions. Our results showed that 2D growth of the different morphological and functional protonemata apical growing cells, chloronema and caulonema, is differentially modulated by this process. These differences depend on the protonema cell type and position along the protonemal filament, and growth condition. As a global plant response, the absence of autophagy favors the spread of the colony through protonemata growth at the expense of a reduction of the 3D growth, such as the buds and gametophore development, and thus the adult gametophytic and reproductive phases. Altogether this study provides valuable information suggesting that autophagy has roles during apical growth with differential responses within the cell types of the same tissue and contributes to life cycle progression and thus the growth and development of the 2D and 3D tissues of P. patens.

Know when and how to die: gaining insights into the molecular regulation of leaf senescence

Senescence is the ultimate phase in the life cycle of leaves which is crucial for recycling of nutrients to maintain plant fitness and reproductive success. The earliest visible manifestation of leaf senescence is their yellowing, which usually commences with the breakdown of chlorophyll. The degradation process involves a gradual and highly coordinated disassembly of macromolecules resulting in the accumulation of nutrients, which are subsequently mobilized from the senescing leaves to the developing organs. Leaf senescence progresses under overly tight genetic and molecular control involving a well-orchestrated and intricate network of regulators that coordinate spatio-temporally with the influence of both internal and external cues. Owing to the advancements in omics technologies, the availability of mutant resources, scalability of molecular analyses methodologies and the advanced capacity to integrate multidimensional data, our understanding of the genetic and molecular basis of leaf ageing has greatly expanded. The review provides a compilation of the multitier regulation of senescence process and the interrelation between the environment and the terminal phase of leaf development. The knowledge gained would benefit in devising the strategies for manipulation of leaf senescence process to improve crop quality and productivity.