A barley homolog of yeast ATG6 is involved in multiple abiotic stress responses and stress resistance regulation

PbrATG6 modulates reactive oxygen species metabolism and interacts with PbrTLP15 synergistic enhancement of pear resistance to Botryosphaeria dothidea

Autophagy is vital for plant defense against pathogens, with ATG6 being a key gene in this process. At present, little has been reported on the potential function and molecular mechanisms of ATG6 mediated pathogen resistance in pear. This study investigates the function of the pear homolog of ATG6 (PbrATG6) in resistance to Botryosphaeria dothidea. PbrATG6 is expressed differentially in pear tissues and its expression increases upon infection. Overexpression of PbrATG6 enhances resistance in Arabidopsis and pear calli, while silencing it increases susceptibility. PbrTLP15, a pathogenesis-related protein belonging to the PR5 family, was found that interacts with PbrATG6 by a yeast two-hybrid screening. Yeast two-hybrid, luciferase complementation imaging, bimolecular fluorescence complementation assays and pull-down assays showed that PbrATG6 interacts with PbrTLP15. The transient silencing transgenic assays of PbrATG6 and PbrTLP15 revealed that PbrATG6 could cooperate with PbrTLP15 to regulate pear B. dothidea resistance. In addition, transcriptional analyses of autophagy key genes in pTRV-PbrTLP15 and transmission electron microscopy (TEM) assays also implied that PbrTLP15 does affect autophagy. Hence, PbrATG6 and PbrTLP15 may synergistically enhance pear B. dothidea disease resistance. It provides a new strategy for the study of autophagy in pear disease resistance and enriches the research on pear disease resistance mechanism.

Evaluation of maize varieties via multivariate analysis: Roles of ionome, antioxidants, and autophagy in salt tolerance

Salt stress presents a major obstacle to maize (Zea mays L.) production globally, impeding its growth and development. In this study, we aimed to identify salt-tolerant maize varieties through evaluation using multivariate analysis and shed light on the role of ionome, antioxidant capacity, and autophagy in salt tolerance. We investigated multiple growth indices, including shoot fresh weight, shoot dry weight, plant height, chlorophyll content, electrolyte leakage, potassium and sodium contents, and potassium-to-sodium ratio, in 20 maize varieties at the V3 stage under salt stress (200 mm NaCl). The results showed significant differences in the growth indices, accompanied by a wide range in their coefficient of variation, suggesting their suitability for screening salt tolerance. Based on D values, clustering analysis categorized the 20 varieties into 4 distinct groups. TG88, KN20, and LR888 (group I) emerged as the most salt-tolerant varieties, while YD9, XD903, and LH151 (group IV) were identified as the most sensitive. TG88 showcased nutrient preservation and redistribution under salt stress, surpassing YD9. It maintained nitrogen and iron levels in roots, while YD9 experienced decreases. TG88 redistributed more nitrogen, zinc, and potassium to its leaves, outperforming YD9. TG88 preserved sulfur levels in both roots and leaves, unlike YD9. Additionally, TG88 demonstrated higher enzymatic antioxidant capacity (superoxide dismutase, peroxidase, ascorbate peroxidase, and glutathione reductase) at both the enzyme and gene expression levels, upregulation of autophagy-related (ATG) genes (ZmATG6, ZmATG8a, and ZmATG10), and increased autophagic activity. Overall, this study offers insights into accurate maize varieties evaluation methods and the physiological mechanisms underlying salt tolerance and identifies promising materials for further research.

Identification of autophagy gene family in potato and the role of StATG8a in salt and drought stress

Autophagy is a highly conserved method of recycling cytoplasm components in eukaryotes. It plays an important role in plant growth and development, as well as in response to biotic and abiotic stresses. Although autophagy-related genes (ATGs) have been identified in several crop species, their particular role in potato (Solanum tuberosum L.) remains unclear. Several transcription factors and signaling genes in the transgenic lines of the model plant Arabidopsis thaliana, such as AtTSPO, AtBES1, AtPIP2;7, AtCOST1 as well as AtATI1/2, ATG8f, GFP-ATG8F-HA, AtDSK2, AtNBR1, AtHKT1 play crucial functions under drought and salt stresses, respectively. In this study, a total of 29 putative StATGs from 15 different ATG subfamilies in the potato genome were identified. Their physicochemical properties, evolutionary connections, chromosomal distribution, gene duplication, protein-protein interaction network, conserved motifs, gene structure, interspecific collinearity relationship, and cis-regulatory elements were analyzed. The results of qRT-PCR detection of StATG expression showed that 29 StATGs were differentially expressed in potato's leaves, flowers, petiole, stem, stolon, tuber, and root. StATGs were dynamically modulated by salt and drought stresses and up-regulated under salt and drought conditions. Our results showed that the StATG8a localized in the cytoplasm and the nucleus. Potato cultivar "Atlantic" overexpressing or downregulating StATG8a were constructed. Based on physiological, biochemical, and photosynthesis parameters, potato lines overexpressing StATG8a exhibited 9 times higher drought and salt tolerance compared to non-transgenic plants. In contrast, the potato plants with knockdown expression showed a downtrend in drought and salt tolerance compared to non-transgenic potato lines. These results could provide new insights into the function of StATG8a in salt and drought response and its possible mechanisms.

Comprehensive Analysis of Autophagy-Related Genes in Rice Immunity against Magnaporthe oryzae

Rice blast disease, caused by the fungus Magnaporthe oryzae, is a significant threat to rice production. Resistant cultivars can effectively resist the invasion of M. oryzae. Thus, the identification of disease-resistant genes is of utmost importance for improving rice production. Autophagy, a cellular process that recycles damaged components, plays a vital role in plant growth, development, senescence, stress response, and immunity. To understand the involvement of autophagy-related genes (ATGs) in rice immune response against M. oryzae, we conducted a comprehensive analysis of 37 OsATGs, including bioinformatic analysis, transcriptome analysis, disease resistance analysis, and protein interaction analysis. Bioinformatic analysis revealed that the promoter regions of 33 OsATGs contained cis-acting elements responsive to salicylic acid (SA) or jasmonic acid (JA), two key hormones involved in plant defense responses. Transcriptome data showed that 21 OsATGs were upregulated during M. oryzae infection. Loss-of-function experiments demonstrated that OsATG6c, OsATG8a, OsATG9b, and OsATG13a contribute to rice blast resistance. Additionally, through protein interaction analysis, we identified five proteins that may interact with OsATG13a and potentially contribute to plant immunity. Our study highlights the important role of autophagy in rice immunity and suggests that OsATGs may enhance resistance to rice blast fungus through the involvement of SA, JA, or immune-related proteins. These findings provide valuable insights for future efforts in improving rice production through the identification and utilization of autophagy-related genes.

VvATG6 contributes to copper stress tolerance by enhancing the antioxidant ability in transgenic grape calli

Autophagy, a conserved degradation and reuse process, plays a crucial role in plant cellular homeostasis during abiotic stress. Although numerous autophagy-related genes (ATGs) that regulate abiotic stress have been identified, few functional studies have shown how they confer tolerance to copper (Cu) stress. Here, we cloned a novel Vitis vinifera ATG6 gene (VvATG6) which was induced by 0.5 and 10 mM Cu stress based on transcriptomic data, and transgenic Arabidopsis thaliana, tobacco (Nicotiana tabacum), and grape calli were successfully obtained through Agrobacterium-mediated genetic transformation. The overexpression of VvATG6 enhanced the tolerance of transgenic lines to Cu. After Cu treatment, the lines that overexpressed VvATG6 grew better and increased their production of biomass compared with the wild-type. These changes were accompanied by higher activities of antioxidant enzymes and a lower accumulation of deleterious malondialdehyde and hydrogen peroxide in the transgenic plants. The activities of superoxide dismutase, peroxidase, and catalase were enhanced owing to the elevation of corresponding antioxidant gene expression in the VvATG6 overexpression plants under Cu stress, thereby promoting the clearance of reactive oxygen species (ROS). Simultaneously, there was a decrease in the levels of expression of RbohB and RbohC that are involved in ROS synthesis in transgenic plants under Cu stress. Thus, the accelerated removal of ROS and the inhibition of its synthesis led to a balanced ROS homeostasis environment, which alleviated the damage from Cu. This could benefit from the upregulation of other ATGs that are necessary for the production of autophagosomes under Cu stress. To our knowledge, this study is the first to demonstrate the protective role of VvATG6 in the Cu tolerance of plants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01415-y.

Drought and recovery in barley: key gene networks and retrotransposon response

Introduction

During drought, plants close their stomata at a critical soil water content (SWC), together with making diverse physiological, developmental, and biochemical responses.

Methods

Using precision-phenotyping lysimeters, we imposed pre-flowering drought on four barley varieties (Arvo, Golden Promise, Hankkija 673, and Morex) and followed their physiological responses. For Golden Promise, we carried out RNA-seq on leaf transcripts before and during drought and during recovery, also examining retrotransposon BARE1expression. Transcriptional data were subjected to network analysis.

Results

The varieties differed by their critical SWC (ϴ_crit), Hankkija 673 responding at the highest and Golden Promise at the lowest. Pathways connected to drought and salinity response were strongly upregulated during drought; pathways connected to growth and development were strongly downregulated. During recovery, growth and development pathways were upregulated; altogether, 117 networked genes involved in ubiquitin-mediated autophagy were downregulated.

Discussion

The differential response to SWC suggests adaptation to distinct rainfall patterns. We identified several strongly differentially expressed genes not earlier associated with drought response in barley. BARE1 transcription is strongly transcriptionally upregulated by drought and downregulated during recovery unequally between the investigated cultivars. The downregulation of networked autophagy genes suggests a role for autophagy in drought response; its importance to resilience should be further investigated.

Barley yellow dwarf Virus-GAV movement protein activating wheat TaATG6-Mediated antiviral autophagy pathway

Barley yellow dwarf virus-GAV (BYDV-GAV) is a highly destructive virus that is transmitted by aphids and can cause substantial yield losses in crops such as wheat (Triticum aestivum), barley (Hordeum vulgare) and oat (Avena sativa). Autophagy is an evolutionarily conserved degradation process that eliminates damaged or harmful intracellular substances during stress conditions or specific developmental processes. However, the mechanism of autophagy involved in disease resistance in wheat remains unknown. In this study, we demonstrate that BYDV-GAV infection could induces the upregulation of genes related to the autophagy pathway in wheat, accompanied by the production of autophagosomes. Furthermore, we confirmed the direct interaction between the viral movement protein (MP) and wheat autophagy-related gene 6 (TaATG6) both in vivo and in vitro. Through yeast function complementation experiments, we determined that TaATG6 can restore the autophagy function in a yeast mutant, atg6. Additionally, we identified the interaction between TaATG6 and TaATG8, core factors of the autophagic pathway, using the yeast two-hybrid system. TaATG6 and TaATG8-silenced wheat plants exhibited a high viral content. Overall, our findings suggest that wheat can recognize BYDV-GAV infection and activate the MP-TaATG6-TaATG8 regulatory network of defense responses through the induction of the autophagy pathway.

Genome-Wide Identification of ATG Gene Family Members in Fagopyrum tataricum and Their Expression during Stress Responses

Abiotic stresses such as drought and salinity are major environmental factors limiting plant productivity. Autophagy-related genes are extensively involved in plant growth, development, and adverse stress responses, which have not yet been characterized in Tartary buckwheat (Fagopyrum tataricum, TB). In this study, we verified that drought stress could induce autophagy in TB roots. Next, 49 FtATGs in the whole genome of TB were identified. All FtATGs were randomly distributed in 8 known chromosomes, while 11 FtATGs were predictably segmental repeats. As the core component of autophagy, there were 8 FtATG8s with similar gene structures in TB, while FtATG8s showed high expression at the transcription level under drought and salt stresses. The cis-acting element analysis identified that all FtATG8 promoters contain light-responsive and MYB-binding elements. FtATG8s showed a cell-wide protein interaction network and strongly correlated with distinct stress-associated transcription factors. Furthermore, overexpression of FtATG8a and FtATG8f enhanced the antioxidant enzyme activities of TB under adverse stresses. Remarkably, FtATG8a and FtATG8f may be vital candidates functioning in stress resistance in TB. This study prominently aids in understanding the biological role of FtATG genes in TB.

Autophagy in the Lifetime of Plants: From Seed to Seed

Autophagy is a highly conserved self-degradation mechanism in eukaryotes. Excess or harmful intracellular content can be encapsulated by double-membrane autophagic vacuoles and transferred to vacuoles for degradation in plants. Current research shows three types of autophagy in plants, with macroautophagy being the most important autophagic degradation pathway. Until now, more than 40 autophagy-related (ATG) proteins have been identified in plants that are involved in macroautophagy, and these proteins play an important role in plant growth regulation and stress responses. In this review, we mainly introduce the research progress of autophagy in plant vegetative growth (roots and leaves), reproductive growth (pollen), and resistance to biotic (viruses, bacteria, and fungi) and abiotic stresses (nutrients, drought, salt, cold, and heat stress), and we discuss the application direction of plant autophagy in the future.

Reverse genetic approaches for breeding nutrient-rich and climate-resilient cereal and food legume crops

In the last decade, advancements in genomics tools and techniques have led to the discovery of many genes. Most of these genes still need to be characterized for their associated function and therefore, such genes remain underutilized for breeding the next generation of improved crop varieties. The recent developments in different reverse genetic approaches have made it possible to identify the function of genes controlling nutritional, biochemical, and metabolic traits imparting drought, heat, cold, salinity tolerance as well as diseases and insect-pests. This article focuses on reviewing the current status and prospects of using reverse genetic approaches to breed nutrient-rich and climate resilient cereal and food legume crops.

Responses of Microstructure, Ultrastructure and Antioxidant Enzyme Activity to PEG-Induced Drought Stress in Cyclocarya paliurus Seedlings

Drought is one of the most important abiotic constraints on agricultural productivity, while global warming leads to the occurrence of more frequent drought events. Cyclocarya paliurus is a multiple-function tree species with medicinal value and timber production, but no information is available on its drought tolerance. In this hydroponic experiment, variations in leaf anatomical morphology, chloroplast ultrastructure, stomatal characteristics, and antioxidant enzyme activities were investigated under six levels of polyethylene glycol 6000 (PEG)-induced drought treatments to assess the drought adaption and physiological response of C. paliurus seedlings. The results showed that PEG-induced drought treatments reduced leaf epidermis, spongy tissue, leaf vein diameter, and spongy ratio, whereas the ratio of palisade tissue to spongy tissue, cell tense ratio, and vein protuberant degree all increased with enhancing the PEG6000 concentrations. Significant differences in stomatal width, stomatal aperture, and stomatal density existed among the treatments (p < 0.01). The stomatal aperture decreased significantly with the increase in PEG6000 concentrations, whereas the greatest stomatal density was observed in the 15% PEG6000 treatment. Compared with the control, higher drought stresses (20% and 25% PEG concentrations) caused damage at the cellular level and chloroplast lysis occurred. PEG6000 treatments also promoted the activities of SOD, POD, and CAT in C. paliurus seedlings, but this increase was insufficient to deal with the membrane lipid peroxidative damage under the high PEG concentrations. Correlation analysis indicated that in most cases there were significant relationships between leaf anatomical characteristics and antioxidant enzyme activities. Our results suggested that C. paliurus seedlings would not survive well when the PEG6000 concentration was over 15% (equal to soil water potential of −0.30 MPa).

Linking Autophagy to Potential Agronomic Trait Improvement in Crops

Autophagy is an evolutionarily conserved catabolic process in eukaryotic cells, by which the superfluous or damaged cytoplasmic components can be delivered into vacuoles or lysosomes for degradation and recycling. Two decades of autophagy research in plants uncovers the important roles of autophagy during diverse biological processes, including development, metabolism, and various stress responses. Additionally, molecular machineries contributing to plant autophagy onset and regulation have also gradually come into people’s sights. With the advancement of our knowledge of autophagy from model plants, autophagy research has expanded to include crops in recent years, for a better understanding of autophagy engagement in crop biology and its potentials in improving agricultural performance. In this review, we summarize the current research progress of autophagy in crops and discuss the autophagy-related approaches for potential agronomic trait improvement in crop plants.

CRISPR/Cas9-Mediated Editing of Autophagy Gene 6 in Petunia Decreases Flower Longevity, Seed Yield, and Phosphorus Remobilization by Accelerating Ethylene Production and Senescence-Related Gene Expression

Developmental petal senescence is a type of programmed cell death (PCD), during which the production of ethylene is induced, the expression of PCD-related genes is upregulated, and nutrients are recycled. Autophagy is an intracellular mechanism involved in PCD modulation and nutrient cycling. As a central component of the autophagy pathway, Autophagy Gene 6 (ATG6) was previously shown as a negative regulator of petal senescence. To better understand the role of autophagy in ethylene biosynthesis and nutrient remobilization during petal senescence, we generated and characterized the knockout (KO) mutants of PhATG6 using CRISPR/Cas9 in Petunia × hybrida 'Mitchell Diploid.' PhATG6-KO lines exhibited decreased flower longevity when compared to the flowers of the wild-type or a non-mutated regenerative line (controls), confirming the negative regulatory role of ATG6 in petal senescence. Smaller capsules and fewer seeds per capsule were produced in the KO plants, indicating the crucial function of autophagy in seed production. Ethylene production and ethylene biosynthesis genes were upregulated earlier in the KO lines than the controls, indicating that autophagy affects flower longevity through ethylene. The transcript levels of petal PCD-related genes, including PhATG6, PhATG8d, PhPI3K (Phosphatidylinositol 3-Kinase), and a metacaspase gene PhMC1, were upregulated earlier in the corollas of PhATG6-KO lines, which supported the accelerated PCD in the KO plants. The remobilization of phosphorus was reduced in the KO lines, showing that nutrient recycling was compromised. Our study demonstrated the important role of autophagy in flower lifespan and seed production and supported the interactions between autophagy and various regulatory factors during developmental petal senescence.

Identification of New ATG8s-Binding Proteins with Canonical LC3-Interacting Region in Autophagosomes of Barley Callus

Autophagy is essential to maintain cellular homeostasis for normal cell growth and development. In selective autophagy, ATG8 plays a crucial role in cargo target recognition by binding to various adaptors and receptors with the ATG8-interacting motif, also known as the LC3-interacting region (LIR). However, the process of autophagy in the callus, as a proliferating cell type, is largely unknown. In this study, we overexpressed green fluorescent protein (GFP)-ATG8a and GFP-ATG8b transgenic barley callus and checked their autophagic activities. We identified five new ATG8 candidate interactors containing the canonical LIR motif by using immunoprecipitation coupled with mass spectrometry: RPP3, COPE, NCLN, RAE1, and CTSL. The binding activities between these candidate interactors and ATG8 were further demonstrated in the punctate structure. Notably, RPP3 was colocalized in ATG8-labeled autophagosomes under tunicamycin-induced ER stress. GST pull-down assays showed that the interaction between RPP3 and ATG8 could be prevented by mutating the LIRs region of RPP3 or the LIR docking site (LDS) of ATG8, suggesting that RPP3 directly interacted with ATG8 in an LIR-dependent manner via the LDS. Our findings would provide the basis for further investigations on novel receptors and functions of autophagy in plants, especially in the physiological state of cell de-differentiation.

Autophagy during drought: function, regulation, and potential application

Drought is a major challenge for agricultural production since it causes substantial yield reduction and economic loss. Autophagy is a subcellular degradation and recycling pathway that functions in plant development and responses to many stresses, including drought. In this review, we summarize the current understanding of the function of autophagy and how autophagy is upregulated during drought stress. Autophagy helps plants to survive drought stress, and the mechanistic basis for this is beginning to be elucidated. Autophagy can selectively degrade aquaporins to adjust water permeability, and also degrades excess heme and damaged proteins to reduce their toxicity. In addition, autophagy can degrade regulators or components of hormone signaling pathways to promote stress responses. During drought recovery, autophagy degrades drought-induced proteins to reset the cell status. Autophagy is activated by multiple mechanisms during drought stress. Several transcription factors are induced by drought to upregulate autophagy-related gene expression, and autophagy is also regulated post-translationally through protein modification and stability. Based on these observations, manipulation of autophagy activity may be a promising approach for conferring drought tolerance in plants.

Genome-wide analysis of autophagy-related genes in Medicago truncatula highlights their roles in seed development and response to drought stress

Autophagy is a highly conserved process of degradation of cytoplasmic constituents in eukaryotes. It is involved in the growth and development of plants, as well as in biotic and abiotic stress response. Although autophagy-related (ATG) genes have been identified and characterized in many plant species, little is known about this process in Medicago truncatula. In this study, 39 ATGs were identified, and their gene structures and conserved domains were systematically characterized in M. truncatula. Many cis-elements, related to hormone and stress responsiveness, were identified in the promoters of MtATGs. Phylogenetic and interaction network analyses suggested that the function of MtATGs is evolutionarily conserved in Arabidopsis and M. truncatula. The expression of MtATGs, at varied levels, was detected in all examined tissues. In addition, most of the MtATGs were highly induced during seed development and drought stress, which indicates that autophagy plays an important role in seed development and responses to drought stress in M. truncatula. In conclusion, this study gives a comprehensive overview of MtATGs and provides important clues for further functional analysis of autophagy in M. truncatula.

Manipulating a Single Transcription Factor, Ant1, Promotes Anthocyanin Accumulation in Barley Grains

Barley has abundant anthocyanin-rich accessions, which renders it an ideal model to investigate the regulatory mechanism of anthocyanin biosynthesis. This study functionally characterized two transcription factors: Ant1 and Ant2. Sequence alignment showed that the coding sequences of Ant1 and Ant2 are conserved among 11 colored hulless barley and noncolored barley varieties. The expression profiles of Ant1 and Ant2 were divergent between species, and significantly higher expression was found in two colored Qingke accessions. The co-expression of Ant1 and Ant2 resulted in purple pigmentation in transient transformation systems via the promotion of the transcription of four structural genes. Ant1 interacted with Ant2, and overexpression of Ant1 activated the transcription of Ant2. Moreover, overexpression of Ant1 led to anthocyanin accumulation in the pericarp and aleurone layer of transgenic barley grains. Overall, our results suggest that anthocyanin-enriched barley grains can be produced by manipulating Ant1 expression.

Autophagy in Plant Abiotic Stress Management

Plants can be considered an open system. Throughout their life cycle, plants need to exchange material, energy and information with the outside world. To improve their survival and complete their life cycle, plants have developed sophisticated mechanisms to maintain cellular homeostasis during development and in response to environmental changes. Autophagy is an evolutionarily conserved self-degradative process that occurs ubiquitously in all eukaryotic cells and plays many physiological roles in maintaining cellular homeostasis. In recent years, an increasing number of studies have shown that autophagy can be induced not only by starvation but also as a cellular response to various abiotic stresses, including oxidative, salt, drought, cold and heat stresses. This review focuses mainly on the role of autophagy in plant abiotic stress management.

Potential Biotechnological Applications of Autophagy for Agriculture

Autophagy is a genetically regulated, eukaryotic cellular degradation system that sequestrates cytoplasmic materials in specialised vesicles, termed autophagosomes, for delivery and breakdown in the lysosome or vacuole. In plants, autophagy plays essential roles in development (e.g., senescence) and responses to abiotic (e.g., nutrient starvation, drought and oxidative stress) and biotic stresses (e.g., hypersensitive response). Initially, autophagy was considered a non-selective bulk degradation mechanism that provides energy and building blocks for homeostatic balance during stress. Recent studies, however, reveal that autophagy may be more subtle and selectively target ubiquitylated protein aggregates, protein complexes and even organelles for degradation to regulate vital cellular processes even during favourable conditions. The selective nature of autophagy lends itself to potential manipulation and exploitation as part of designer protein turnover machinery for the development of stress-tolerant and disease-resistant crops, crops with increased yield potential and agricultural efficiency and reduced post-harvest losses. Here, we discuss our current understanding of autophagy and speculate its potential manipulation for improved agricultural performance.

Silencing ATG6 and PI3K accelerates petal senescence and reduces flower number and shoot biomass in petunia

Petal senescence is a form of developmental programmed cell death (PCD) that is regulated by internal and environmental signals. Autophagy, a metabolic pathway that regulates intercellular nutrient recycling, is thought to play an important role in the regulation of petal senescence-associated PCD. To characterize the function of two central autophagy genes in petal senescence, we down-regulated Autophagy Gene 6 (PhATG6) and Phosphoinositide 3-Kinase (PhPI3K) using Virus-Induced Gene Silencing (VIGS) in Petunia × hybrida. The silencing of PhATG6 and PhPI3K accelerated petal senescence, thereby reducing flower longevity. Both PhATG6- and PhPI3K-silenced petunias had reduced flower numbers, flower biomass, and vegetative shoot biomass. These phenotypes were intensified when plants were grown under low nutrient conditions. Additionally, two important regulators of senescence, an ethylene biosynthesis gene (PhACS) and a type I metacaspase gene (PhMC1), were suppressed in senescing petals of PhATG6- and PhPI3K-silenced plants. In conclusion, our study identified PhATG6 and PhPI3K as negative regulators of flower senescence and demonstrated the influence of nutrient limitation on the function of autophagy during petal senescence. Our study also found that autophagy genes potentially influence the transcriptional regulation of metacaspases and ethylene biosynthetic genes during petal senescence. The results of this project will be fundamental for future studies of petal senescence and will provide genetic information for future crop improvement.

Autophagy and Its Regulators in Response to Stress in Plants

To survive in stressful conditions, plants have developed multiple strategies to relieve damage. One of the strategies is to clear the damaged protein and organelles. Autophagy is a highly conservative degradation process, which refers to the recycling of damaged protein and organelles. Over the past decades, increasing evidence has revealed the important roles of autophagy in response to stress conditions, and many factors have been revealed involved in the sophisticated regulation of the autophagy signaling pathway. However, the accurate regulation pathway of the autophagy pathway is largely unknown. The current review proposes how stress-response factors respond to stress conditions involved in regulating the autophagy signaling pathway. In short, clarifying the regulating pathway of autophagy in response to stress conditions is beneficial to plant breeding.

Transcriptional Plasticity of Autophagy-Related Genes Correlates with the Genetic Response to Nitrate Starvation in Arabidopsis Thaliana

In eukaryotes, autophagy, a catabolic mechanism for macromolecule and protein recycling, allows the maintenance of amino acid pools and nutrient remobilization. For a better understanding of the relationship between autophagy and nitrogen metabolism, we studied the transcriptional plasticity of autophagy genes (ATG) in nine Arabidopsis accessions grown under normal and nitrate starvation conditions. The status of the N metabolism in accessions was monitored by measuring the relative expression of 11 genes related to N metabolism in rosette leaves. The transcriptional variation of the genes coding for enzymes involved in ammonium assimilation characterize the genetic diversity of the response to nitrate starvation. Starvation enhanced the expression of most of the autophagy genes tested, suggesting a control of autophagy at transcriptomic level by nitrogen. The diversity of the gene responses among natural accessions revealed the genetic variation existing for autophagy independently of the nutritive condition, and the degree of response to nitrate starvation. We showed here that the genetic diversity of the expression of N metabolism genes correlates with that of the ATG genes in the two nutritive conditions, suggesting that the basal autophagy activity is part of the integral response of the N metabolism to nitrate availability.

The barley miR393 has multiple roles in regulation of seedling growth, stomatal density, and drought stress tolerance

microRNA393 (miR393) and its target module have been implicated as comprising a conserved mechanism to regulate developmental processes and plant growth in response to environmental signals through the auxin signaling pathway. Our previous work identified miR393 and its two targets in barley. In this study, we further investigated the expression pattern of miR393 and its biological functions in seedling growth and drought tolerance. We showed that the miR393 overexpressing line (OE) exhibited increased stomatal density with decreased guard cell length, while the miR393 knockdown line (MIM) displayed the opposite phenotype, which might be due to the effects of miR393 on AUXIN RESPONSE FACTOR5 (ARF5) and three stomatal development-related genes, such as EPIDERMAL PATTERNING FACTOR1 (EPF1), SPEECHLESS (SPCH), and MUTE. In addition, the MIM line conferred enhanced drought tolerance, with alleviated leaf chlorosis and lipid peroxidation after 22 days drought treatment. In contrast, the OE line was more sensitive to drought stress and accumulated more malondialdehyde and hydrogen peroxide than the wild type. Furthermore, polyethylene glycol (PEG) treatment-induced abscisic acid (ABA) accumulation in leaves was suppressed in the OE line, indicating that miR393 might regulate drought stress response and tolerance through its interaction with ABA biosynthesis. Overall, these data suggest that miR393 might be a potential target for manipulation of stomatal density and improvement of drought tolerance in barley.

Virus-induced gene silencing: empowering genetics in non-model organisms

Virus-induced gene silencing (VIGS) is an RNA interference-based technology used to transiently knock down target gene expression by utilizing modified plant viral genomes. VIGS can be adapted to many angiosperm species that cover large phylogenetic distances, allowing the analysis of gene functions in species that are not amenable to stable genetic transformation. With a vast amount of sequence information already available and even more likely to become available in the future, VIGS provides a means to analyze the functions of candidate genes identified in large genomic or transcriptomic screens. Here, we provide a comprehensive overview of target species and VIGS vector systems, assess recent key publications in the field, and explain how plant viruses are modified to serve as VIGS vectors. As many reports on the VIGS technique are being published, we also propose minimal reporting guidelines for carrying out these experiments, with the aim of increasing comparability between experiments. Finally, we propose methods for the statistical evaluation of phenotypic results obtained with VIGS-treated plants, as analysis is challenging due to the predominantly transient nature of the silencing effect.

24-Epibrassinolide-alleviated drought stress damage influences antioxidant enzymes and autophagy changes in peach (Prunus persicae L.) leaves

Drought stress is a serious threat to agriculture and the environment. Brassinosteroids (BRs) increase tolerance to drought stress of plant. Autophagy plays important roles in plant responses to drought stress; however, there are few reports on autophagy in peach (Prunus persica). In total, 23 putative autophagy-related genes (ATGs) in peach were identified using ATGs from the Arabidopsis thaliana genome as query in BLASTx algorithm-based searches. Under drought stress, the photosynthetic abilities of peach leaves decreased, while antioxidant enzyme activities, autophagy and ATG expression increased. A correlation analysis showed that antioxidant enzyme activities are inversely correlated to the expression levels of the PpATGs. During drought, the PpATG8s and some PpATG18s had the strongest responses. To investigate enhanced drought-stress tolerance, peach was treated with water, 100 nM 24-epibrassinolide (EBR), 1 μM EBR, 10 μM EBR and 1 μM voriconazole. Exogenous EBR at 1 μM decreased the malondialdehyde (MDA) content under drought stress when compared with water-, 1 μM voriconazole-, 100 nM EBR- and 10 μM EBR-treated peach leaf. The 1-μM EBR application increased superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and glutathione peroxidase (GR) activities during drought stress. In addition, the expression levels of PpATGs were inhibited by EBR. Thus, the 1-μM EBR treatment alleviated drought-stress damage to peach leaves, decreased PpATG expression levels and reduced the number of autophagosomes.

Autophagy in crop plants: what's new beyond Arabidopsis?

Autophagy is a major degradation and recycling pathway in plants. It functions to maintain cellular homeostasis and is induced by environmental cues and developmental stimuli. Over the past decade, the study of autophagy has expanded from model plants to crop species. Many features of the core machinery and physiological functions of autophagy are conserved among diverse organisms. However, several novel functions and regulators of autophagy have been characterized in individual plant species. In light of its critical role in development and stress responses, a better understanding of autophagy in crop plants may eventually lead to beneficial agricultural applications. Here, we review recent progress on understanding autophagy in crops and discuss potential future research directions.

Milestones achieved in response to drought stress through reverse genetic approaches

Drought stress is the most important abiotic stress that constrains crop production and reduces yield drastically. The germplasm of most of the cultivated crops possesses numerous unknown drought stress tolerant genes. Moreover, there are many reports suggesting that the wild species of most of the modern cultivars have abiotic stress tolerant genes. Due to climate change and population booms, food security has become a global issue. To develop drought tolerant crop varieties knowledge of various genes involved in drought stress is required. Different reverse genetic approaches such as virus-induced gene silencing (VIGS), clustered regularly interspace short palindromic repeat (CRISPR), targeting induced local lesions in genomes (TILLING) and expressed sequence tags (ESTs) have been used extensively to study the functionality of different genes involved in response to drought stress. In this review, we described the contributions of different techniques of functional genomics in the study of drought tolerant genes.