Phytochrome B-mediated activation of lipoxygenase modulates an excess red light-induced defence response in Arabidopsis

Genome-Wide Identification and Expression Analysis of Lipoxygenase Genes in Rose (Rosa chinensis)

Lipoxygenases (LOX) play pivotal roles in plant resistance to stresses. However, no study has been conducted on LOX gene identification at the whole genome scale in rose (Rosa chinensis). In this study, a total of 17 RcLOX members were identified in the rose genome. The members could be classified into three groups: 9-LOX, Type I 13-LOX, and Type II 13-LOX. Similar gene structures and protein domains can be found in RcLOX members. The RcLOX genes were spread among all seven chromosomes, with unbalanced distributions, and several tandem and proximal duplication events were found among RcLOX members. Expressions of the RcLOX genes were tissue-specific, while every RcLOX gene could be detected in at least one tissue. The expression levels of most RcLOX genes could be up-regulated by aphid infestation, suggesting potential roles in aphid resistance. Our study offers a systematic analysis of the RcLOX genes in rose, providing useful information not only for further gene cloning and functional exploration but also for the study of aphid resistance.

Genome-wide identification and expression pattern analysis of lipoxygenase genes of chickpea (Cicer arietinum L.) in response to accelerated aging

Seed aging is a major problem which is caused by various factors such as unfavorable physiological, biochemical, and metabolic alterations in seed cells. Lipoxygenase (LOXs), an oxidoreductase enzyme that catalyzes the oxidation of polyunsaturated fatty acids, acts as a negative regulator in seed viability and vigour during storage. In this study, we identified ten putative LOX gene family members in the chickpea genome, designated as "CaLOX" which are mainly located in the cytoplasm and chloroplast. These genes share different physiochemical properties and similarities in their gene structures and conserved functional regions. The promoter region contained the cis-regulatory elements and transcription binding factors, which were mainly linked to biotic and abiotic stress, hormones, and light responsiveness. In this study, chickpea seeds were treated with accelerated aging treatment for 0, 2, and 4 days at 45°C and 85 % relative humidity. Increased level of reactive oxygen species, malondialdehyde, electrolyte leakage, proline, lipoxygenase (LOX) activity, and decreased catalase activity indicates cellular dysfunction and demonstrated seed deterioration. Quantitative real-time analysis reveals that 6 CaLOX genes were upregulated, and 4 CaLOX genes were downregulated during the seed aging process in chickpea. This comprehensive study will reveal the role of the CaLOX gene in response to aging treatment. The identified gene may be used to develop better-quality seeds in chickpea.

PIF8-WRKY42-mediated salicylic acid synthesis modulates red light induced powdery mildew resistance in oriental melon

Light signals and plant hormones are involved in regulating the growth, development and stress resistance of plants; however, it remains unclear whether light affects hormones and thus pathogen resistance in oriental melon. Here, we found that red light promoted salicylic acid (SA) accumulation and powdery mildew resistance by activating the transcription of CmICS, the key gene for SA biosynthesis, and silencing CmICS seriously weakened the induction effect of red light on powdery mildew resistance in oriental melon leaves. Further studies showed that red light induced the expression of CmWRKY42 under powdery mildew stress, and CmWRKY42 directly bound to the CmICS promoter to activate its expression and promote the accumulation of SA under red light. Furthermore, we found that PHYTOCHROME INTERACTING FACTOR 8 (PIF8), as a negative regulator of SA biosynthesis, inhibits CmWRKY42 transcriptional activation by binding to the CmWRKY42 promoter, and thus inhibits transcriptional activation of CmICS by CmWRKY42. Also, CmPIF8 binds to the CmICS promoter and directly inhibits its transcription. In conclusion, our study revealed a new molecular mechanism of the relationship between red light-SA-powdery mildew resistance and provided a theoretical basis for resistance breeding of oriental melon.

Genetic Dissection of Light-Regulated Adventitious Root Induction in Arabidopsis thaliana Hypocotyls

Photomorphogenic responses of etiolated seedlings include the inhibition of hypocotyl elongation and opening of the apical hook. In addition, dark-grown seedlings respond to light by the formation of adventitious roots (AR) on the hypocotyl. How light signaling controls adventitious rooting is less well understood. Hereto, we analyzed adventitious rooting under different light conditions in wild type and photomorphogenesis mutants in Arabidopsis thaliana. Etiolation was not essential for AR formation but raised the competence to form AR under white and blue light. The blue light receptors CRY1 and PHOT1/PHOT2 are key elements contributing to the induction of AR formation in response to light. Furthermore, etiolation-controlled competence for AR formation depended on the COP9 signalosome, E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC (COP1), the COP1 interacting SUPPRESSOR OF PHYA-105 (SPA) kinase family members (SPA1,2 and 3) and Phytochrome-Interacting Factors (PIF). In contrast, ELONGATED HYPOCOTYL5 (HY5), suppressed AR formation. These findings provide a genetic framework that explains the high and low AR competence of Arabidopsis thaliana hypocotyls that were treated with dark, and light, respectively. We propose that light-induced auxin signal dissipation generates a transient auxin maximum that explains AR induction by a dark to light switch.

Ferroptosis in plants: regulation of lipid peroxidation and redox status

Regulated cell death (RCD) is an essential process that plays key roles along the plant life cycle. Unlike accidental cell death, which is an uncontrolled biological process, RCD involves integrated signaling cascades and precise molecular-mediated mechanisms that are triggered in response to specific exogenous or endogenous stimuli. Ferroptosis is a cell death pathway characterized by the iron-dependent accumulation of lipid reactive oxygen species. Although first described in animals, ferroptosis in plants shares all the main core mechanisms observed for ferroptosis in other systems. In plants as in animals, oxidant and antioxidant systems outline the process of lipid peroxidation during ferroptosis. In plants, cellular compartments such as mitochondria, chloroplasts and cytosol act cooperatively and coordinately to respond to changing redox environments. This particular context makes plants a unique model to study redox status regulation and cell death. In this review, we focus on our most recent understanding of the regulation of redox state and lipid peroxidation in plants and their role during ferroptosis.

Evolution and functional diversity of lipoxygenase (LOX) genes in allotetraploid rapeseed (Brassica napus L.)

Lipoxygenase (LOX, EC 1.13.11.12) is a non-haeme iron-containing dioxygenase family that catalyzes the oxygenation of polyunsaturated fatty acids into bio-functionally fatty acid diverse (oxylipins) and plays vital role in plant growth and development and responses to abiotic and biotic stresses. Though LOX genes have been studied in many plant species, their roles in Brassicaceae species are still unknown. Here, a set of 14, 18, and 33 putative LOX genes were identified in Brassica rapa, Brassica oleracea and Brassica napus (allotetraploid rapeseed), respectively, which could be divided into 9-LOX (LOX1/5), 13-LOX type I (LOX3/4/6), and type II (LOX2) subgroups. There was an expansion of LOX2 orthologous genes in Brassicaceae. Most of the LOX genes are intron rich and conserved in gene structure, and the LOX proteins all have the conserved lipoxygenase and PLAT/LH2 domain. Ka/Ks ratio revealed that the majority of LOXs underwent purifying selection in Brassicaceae. The light-, ABA-, MeJA-related cis-elements and MYB-binding sites in the promoters of BnaLOXs were the most abundant. BnaLOXs displayed different spatiotemporal expression patterns and various abiotic/biotic stress responsive expression patterns. BnaLOX1/5 were slightly or no response to phytohormones and abiotic stresses. BnaLOX3/4/6 predominantly express in roots and were strongly up-regulated by salinity and PEG treatments, and BnaLOX3/4 were the methyl jasmonate (MeJA) and salicylic acid (SA) early response genes and strongly induced by infection of Sclerotinia sclerotiorum; while the BnaLOX2 members predominantly express in stamens, were MeJA and SA continuous response genes and strongly repressed by cold, heat and waterlogging treatments in leaves. Our results are useful for understanding the biological functions of the BnaLOX genes in allotetraploid rapeseed.

Ferroptosis in plants: triggers, proposed mechanisms, and the role of iron in modulating cell death

Regulated cell death plays key roles during essential processes throughout the plant life cycle. It takes part in specific developmental programs and maintains homeostasis of the organism in response to unfavorable environments. Ferroptosis is a recently discovered iron-dependent cell death pathway characterized by the accumulation of lipid reactive oxygen species. In plants, ferroptosis shares all the main hallmarks described in other systems. Those specific features include biochemical and morphological signatures that seem to be conserved among species. However, plant cells have specific metabolic pathways and a high degree of metabolic compartmentalization. Together with their particular morphology, these features add more complexity to the plant ferroptosis pathway. In this review, we summarize the most recent advances in elucidating the roles of ferroptosis in plants, focusing on specific triggers, the main players, and underlying pathways.

Plant Defense Responses to Biotic Stress and Its Interplay With Fluctuating Dark/Light Conditions

Plants are subjected to a plethora of environmental cues that cause extreme losses to crop productivity. Due to fluctuating environmental conditions, plants encounter difficulties in attaining full genetic potential for growth and reproduction. One such environmental condition is the recurrent attack on plants by herbivores and microbial pathogens. To surmount such attacks, plants have developed a complex array of defense mechanisms. The defense mechanism can be either preformed, where toxic secondary metabolites are stored; or can be inducible, where defense is activated upon detection of an attack. Plants sense biotic stress conditions, activate the regulatory or transcriptional machinery, and eventually generate an appropriate response. Plant defense against pathogen attack is well understood, but the interplay and impact of different signals to generate defense responses against biotic stress still remain elusive. The impact of light and dark signals on biotic stress response is one such area to comprehend. Light and dark alterations not only regulate defense mechanisms impacting plant development and biochemistry but also bestow resistance against invading pathogens. The interaction between plant defense and dark/light environment activates a signaling cascade. This signaling cascade acts as a connecting link between perception of biotic stress, dark/light environment, and generation of an appropriate physiological or biochemical response. The present review highlights molecular responses arising from dark/light fluctuations vis-à-vis elicitation of defense mechanisms in plants.

Prediction of condition-specific regulatory genes using machine learning

Recent advances in genomic technologies have generated data on large-scale protein–DNA interactions and open chromatin regions for many eukaryotic species. How to identify condition-specific functions of transcription factors using these data has become a major challenge in genomic research. To solve this problem, we have developed a method called ConSReg, which provides a novel approach to integrate regulatory genomic data into predictive machine learning models of key regulatory genes. Using Arabidopsis as a model system, we tested our approach to identify regulatory genes in data sets from single cell gene expression and from abiotic stress treatments. Our results showed that ConSReg accurately predicted transcription factors that regulate differentially expressed genes with an average auROC of 0.84, which is 23.5–25% better than enrichment-based approaches. To further validate the performance of ConSReg, we analyzed an independent data set related to plant nitrogen responses. ConSReg provided better rankings of the correct transcription factors in 61.7% of cases, which is three times better than other plant tools. We applied ConSReg to Arabidopsis single cell RNA-seq data, successfully identifying candidate regulatory genes that control cell wall formation. Our methods provide a new approach to define candidate regulatory genes using integrated genomic data in plants.

Identification of Callose Synthases in Stinging Nettle and Analysis of Their Expression in Different Tissues

Callose is an important biopolymer of β-1,3-linked glucose units involved in different phases of plant development, reproduction and response to external stimuli. It is synthesized by glycosyltransferases (GTs) known as callose synthases (CalS) belonging to family 48 in the Carbohydrate-Active enZymes (CAZymes) database. These GTs are anchored to the plasma membrane via transmembrane domains. Several genes encoding CalS have been characterized in higher plants with 12 reported in the model organism Arabidopsis thaliana. Recently, the de novo transcriptome of a fibre-producing clone of stinging nettle (Urtica dioica L.) was published and here it is mined for CalS genes with the aim of identifying members differentially expressed in the core and cortical tissues of the stem. The goal is to understand whether specific CalS genes are associated with distinct developmental stages of the stem internodes (elongation, thickening). Nine genes, eight of which encoding full-length CalS, are identified in stinging nettle. The phylogenetic analysis with CalS proteins from other fibre crops, namely textile hemp and flax, reveals grouping into 6 clades. The expression profiles in nettle tissues (roots, leaves, stem internodes sampled at different heights) reveal differences that are most noteworthy in roots vs. leaves. Two CalS are differentially expressed in the internodes sampled at the top and middle of the stem. Implications of their role in nettle stem tissue development are discussed.

Genome-wide identification of mitogen-activated protein kinase (MAPK) cascade and expression profiling of CmMAPKs in melon (Cucumis melo L.)

Mitogen-activated protein kinase (MAPK) is a form of serine/threonine protein kinase that activated by extracellular stimulation acting through the MAPK cascade (MAPKKK-MAPKK-MAPK). The MAPK cascade gene family, an important family of protein kinases, plays a vital role in responding to various stresses and hormone signal transduction processes in plants. In this study, we identified 14 CmMAPKs, 6 CmMAPKKs and 64 CmMAPKKKs in melon genome. Based on structural characteristics and a comparison of phylogenetic relationships of MAPK gene families from Arabidopsis, cucumber and watermelon, CmMAPKs and CmMAPKKs were categorized into 4 groups, and CmMAPKKKs were categorized into 3 groups. Furthermore, chromosome location revealed an unevenly distribution on chromosomes of MAPK cascade genes in melon, respectively. Eventually, qRT-PCR analysis showed that all 14 CmMAPKs had different expression patterns under drought, salt, salicylic acid (SA), methyl jasmonate (MeJA), red light (RL), and Podosphaera xanthii (P. xanthii) treatments. Overall, the expression levels of CmMAPK3 and CmMAPK7 under different treatments were higher than those in control. Our study provides an important basis for future functional verification of MAPK genes in regulating responses to stress and signal substance in melon.

The RhHB1/RhLOX4 module affects the dehydration tolerance of rose flowers (Rosa hybrida) by fine-tuning jasmonic acid levels

Phytohormones are key factors in plant responsiveness to abiotic and biotic stresses, and maintaining hormone homeostasis is critically important during stress responses. Cut rose (Rosa hybrida) flowers experience dehydration stress during postharvest handling, and jasmonic acid (JA) levels change as a result of this stress. However, how JA is involved in dehydration tolerance remains unclear. We investigated the functions of the JA- and dehydration-induced RhHB1 gene, which encodes a homeodomain-leucine zipper I γ-clade transcription factor, in rose flowers. Silencing RhHB1 decreased petal dehydration tolerance and resulted in a persistent increase in JA-Ile content and reduced dehydration tolerance. An elevated JA-Ile level had a detrimental effect on rose petal dehydration tolerance. RhHB1 was shown to lower the transient induction of JA-Ile accumulation in response to dehydration. In addition to transcriptomic data, we obtained evidence that RhHB1 suppresses the expression of the lipoxygenase 4 (RhLOX4) gene by directly binding to its promoter both in vivo and in vitro. We propose that increased JA-Ile levels weaken the capacity for osmotic adjustment in petal cells, resulting in reduced dehydration tolerance. In conclusion, a JA feedback loop mediated by an RhHB1/RhLOX4 regulatory module provides dehydration tolerance by fine-tuning bioactive JA levels in dehydrated flowers.

Isolation and functional validation of the CmLOX08 promoter associated with signalling molecule and abiotic stress responses in oriental melon, Cucumis melo var. makuwa Makino

BACKGROUND

Lipoxygenases (LOXs) play significant roles in abiotic stress responses, and identification of LOX gene promoter function can make an important contribution to elucidating resistance mechanisms. Here, we cloned the CmLOX08 promoter of melon (Cucumis melo) and identified the main promoter regions regulating transcription in response to signalling molecules and abiotic stresses.

RESULTS

The 2054-bp promoter region of CmLOX08 from melon leaves was cloned, and bioinformatic analysis revealed that it harbours numerous cis-regulatory elements associated with signalling molecules and abiotic stress. Five 5'-deletion fragments obtained from the CmLOX08 promoter-2054 (LP1), 1639 (LP2), 1284 (LP3), 1047 (LP4), and 418 bp (LP5)-were fused with a GUS reporter gene and used for tobacco transient assays. Deletion analysis revealed that in response to abscisic acid, salicylic acid, and hydrogen peroxide, the GUS activity of LP1 was significantly higher than that of the mock-treated control and LP2, indicating that the - 2054- to - 1639-bp region positively regulates expression induced by these signalling molecules. However, no deletion fragment GUS activity was induced by methyl jasmonate. In response to salt, drought, and wounding treatments, LP1, LP2, and LP4 promoted significantly higher GUS expression compared with the control. Among all deletion fragments, LP4 showed the highest GUS expression, indicating that - 1047 to - 1 bp is the major region regulating promoter activity and that the - 1047 to - 418-bp region positively regulates expression induced by salt, drought, and wounding, whereas the - 1284 to - 1047-bp region is a negative regulatory segment. Interestingly, although the GUS activity of LP1 and LP2 was not affected by temperature changes, that of LP3 was significantly induced by heat, indicating that the - 1284- to - 1-bp region is a core sequence responding to heat and the - 2054- to - 1284-bp region negatively regulates expression induced by heat. Similarly, the - 1047- to - 1-bp region is the main sequence responding to cold, whereas the - 2054- to - 1047-bp region negatively regulates expression induced by cold.

CONCLUSIONS

We cloned the CmLOX08 promoter and demonstrated that it is a signalling molecule/stress-inducible promoter. Furthermore, we identified core and positive/negative regulatory regions responding to three signalling molecules and five abiotic stresses.

ARSENATE INDUCED CHLOROSIS 1/ TRANSLOCON AT THE OUTER ENVOLOPE MEMBRANE OF CHLOROPLASTS 132 Protects Chloroplasts from Arsenic Toxicity

Arsenic (As) is highly toxic to plants and detoxified primarily through complexation with phytochelatins (PCs) and other thiol compounds. To understand the mechanisms of As toxicity and detoxification beyond PCs, we isolated an arsenate-sensitive mutant of Arabidopsis (Arabidopsis thaliana), arsenate induced chlorosis1 (aic1), in the background of the PC synthase-defective mutant cadmium-sensitive1-3 (cad1-3). Under arsenate stress, aic1 cad1-3 showed larger decreases in chlorophyll content and the number and size of chloroplasts than cad1-3 and a severely distorted chloroplast structure. The aic1 single mutant also was more sensitive to arsenate than the wild type (Columbia-0). As concentrations in the roots, shoots, and chloroplasts were similar between aic1 cad1-3 and cad1-3 Using genome resequencing and complementation, TRANSLOCON AT THE OUTER ENVOLOPE MEMBRANE OF CHLOROPLAST132 (TOC132) was identified as the mutant gene, which encodes a translocon protein involved in the import of preproteins from the cytoplasm into the chloroplasts. Proteomic analysis showed that the proteome of aic1 cad1-3 chloroplasts was more affected by arsenate stress than that of cad1-3 A number of proteins related to chloroplast ribosomes, photosynthesis, compound synthesis, and thioredoxin systems were less abundant in aic1 cad1-3 than in cad1-3 under arsenate stress. Our results indicate that chloroplasts are a sensitive target of As toxicity and that AIC1/Toc132 plays an important role in protecting chloroplasts from As toxicity.

Digital Imaging Combined with Genome-Wide Association Mapping Links Loci to Plant-Pathogen Interaction Traits

Plant resistance to generalist pathogens with broad host ranges, such as Botrytis cinerea (Botrytis), is typically quantitative and highly polygenic. Recent studies have begun to elucidate the molecular genetic basis of plant-pathogen interactions using commonly measured traits, including lesion size and/or pathogen biomass. However, with the advent of digital imaging and high-throughput phenomics, there are a large number of additional traits available to study quantitative resistance. In this study, we used high-throughput digital imaging analysis to investigate previously poorly characterized visual traits of plant-pathogen interactions related to disease resistance using the Arabidopsis (Arabidopsis thaliana)/Botrytis pathosystem. From a large collection of visual lesion trait measurements, we focused on color, shape, and size to test how these aspects of the Arabidopsis/Botrytis interaction are genetically related. Through genome-wide association mapping in Arabidopsis, we show that lesion color and shape are genetically separable traits associated with plant disease resistance. Moreover, by employing defined mutants in 23 candidate genes identified from the genome-wide association mapping, we demonstrate links between loci and each of the different plant-pathogen interaction traits. These results expand our understanding of the functional mechanisms driving plant disease resistance.

Phytochrome B1-dependent control of SP5G transcription is the basis of the night break and red to far-red light ratio effects in tomato flowering

BACKGROUND

Phytochromes are dimeric proteins with critical roles in perceiving day length and the environmental signals that trigger flowering. Night break (NB) and the red to far-red light ratio (R:FR) have been used extensively as tools to study the photoperiodic control of flowering. However, at the molecular level, little is known about the effect of NB and different R:FR values on flowering in day-neutral plants (DNPs) such as tomato.

RESULTS

Here, we show that tomato SP5G, SP5G2, and SP5G3 are homologs of Arabidopsis thaliana FLOWERING LOCUS T (FT) that repress flowering in Nicotiana benthamiana. NB every 2 h at intensities of 10 μmol m- 2 s- 1 or lower R:FR (e.g., 0.6) caused a clear delay in tomato flowering and promoted SP5G mRNA expression. The promoted SP5G mRNA expression induced by red light NB and low R:FR treatments was reversed by a subsequent FR light stimulus or a higher R:FR treatment. The tomato phyB1 mutation abolished the effects of NB and lower R:FR treatments on flowering and SP5G mRNA expression, indicating that the effects were mediated by phytochrome B1 in tomato.

CONCLUSION

Our results strongly suggest that SP5G mRNA suppression is the principal cause of NB and lower R:FR effects on flowering in tomato.

Exposure to lower red to far-red light ratios improve tomato tolerance to salt stress

BACKGROUND

Red (R) and far-red (FR) light distinctly influence phytochrome-mediated initial tomato growth and development, and more recent evidence indicates that these spectra also modulate responses to a multitude of abiotic and biotic stresses. This research investigated whether different R: FR values affect tomato growth response and salinity tolerance. Tomato seedlings were exposed to different R: FR conditions (7.4, 1.2 and 0.8) under salinity stress (100 mM NaCl), and evaluated for their growth, biochemical changes, active reactive oxygen species (ROS) and ROS scavenging enzymes, pigments, rate of photosynthesis, and chlorophyll fluorescence.

RESULTS

The results showed that under conditions of salinity, tomato seedlings subjected to a lower R: FR value (0.8) significantly increased both their growth, proline content, chlorophyll content and net photosynthesis rate (Pn), while they decreased malondialdehyde (MDA) compared to the higher R: FR value (7.4). Under conditions of salinity, the lower R: FR value caused a decrease in both the superoxide anion (O₂^•-) and in hydrogen peroxide (H₂O₂) generation, an increase in the activities of superoxidase dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.7). Tomato seedlings grown under the lower R: FR value and conditions of salinity showed a higher actual quantum yield of photosynthesis (ΦPSII), electron transport rate (ETR), and photochemical quenching (qP) than those exposed to a higher R: FR, indicating overall healthier growth. However, the salinity tolerance induced at the lower R: FR condition disappeared in the tomato phyB1 mutant.

CONLUSION

These results suggest that growing tomato with a lower R: FR value could improve seedlings' salinity tolerance, and phytochrome B1 play an very important role in this process. Therefore, different qualities of light can be used to efficiently develop abiotic stress tolerance in tomato cultivation.

Coordination Between ROS Regulatory Systems and Other Pathways Under Heat Stress and Pathogen Attack

Regulatory systems of reactive oxygen species (ROS) are known to be integrated with other pathways involving Ca²⁺ signaling, protein kinases, hormones and programmed cell death (PCD) pathways to regulate defense mechanisms in plants. Coordination between ROS regulatory systems and other pathways needs to be flexibly modulated to finely tune the mechanisms underlying responses of different types of tissues to heat stress, biotic stresses and their combinations during different growth stages. Especially, modulation of the delicate balance between ROS-scavenging and producing systems in reproductive tissues could be essential, because ROS-dependent PCD is required for the proper fertilization, despite the necessity of ROS scavenging to prevent the damage on cells under heat stress and biotic stresses. In this review, we will update the recent findings associated with coordination between multiple pathways under heat stress, pathogen attack and their combinations. In addition, possible integrations between different signals function in different tissues via ROS-dependent long-distance signals will be proposed.

Cross-talk between high light stress and plant defence to the two-spotted spider mite in Arabidopsis thaliana

Little is known about how plants deal with arthropod herbivores under the fluctuating light intensity and spectra which occur in natural environments. Moreover, the role of simultaneous stress such as excess light (EL) in the regulation of plant responses to herbivores is poorly characterized. In the current study, we focused on a mite-herbivore, specifically, the two-spotted spider mite (TSSM), which is one of the major agricultural pests worldwide. Our results showed that TSSM-induced leaf damage (visualized by trypan blue staining) and oviposition rate (measured as daily female fecundity) decreased after EL pre-treatment in wild-type Arabidopsis plants, but the observed responses were not wavelength specific. Thus, we established that EL pre-treatment reduced Arabidopsis susceptibility to TSSM infestation. Due to the fact that a portion of EL energy is dissipated by plants as heat in the mechanism known as non-photochemical quenching (NPQ) of chlorophyll fluorescence, we tested an Arabidopsis npq4-1 mutant impaired in NPQ. We showed that npq4-1 plants are significantly less susceptible to TSSM feeding activity, and this result was not dependent on light pre-treatment. Therefore, our findings strongly support the role of light in plant defence against TSSM, pointing to a key role for a photo-protective mechanism such as NPQ in this regulation. We hypothesize that plants impaired in NPQ are constantly primed to mite attack, as this seems to be a universal evolutionarily conserved mechanism for herbivores.

De novo Transcriptome Analysis of Rhizoctonia solani AG1 IA Strain Early Invasion in Zoysia japonica Root

Zoysia japonica brown spot was caused by necrotrophic fungus Rhizoctonia solani invasion, which led to severe financial loss in city lawn and golf ground maintenance. However, little was known about the molecular mechanism of R. solani pathogenicity in Z. japonica. In this study we examined early stage interaction between R. solani AG1 IA strain and Z. japonica cultivar “Zenith” root by cell ultra-structure analysis, pathogenesis-related proteins assay and transcriptome analysis to explore molecular clues for AG1 IA strain pathogenicity in Z. japonica. No obvious cell structure damage was found in infected roots and most pathogenesis-related protein activities showedg a downward trend especially in 36 h post inoculation, which exhibits AG1 IA strain stealthy invasion characteristic. According to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) database classification, most DEGs in infected “Zenith” roots dynamically changed especially in three aspects, signal transduction, gene translation, and protein synthesis. Total 3422 unigenes of “Zenith” root were predicted into 14 kinds of resistance (R) gene class. Potential fungal resistance related unigenes of “Zenith” root were involved in ligin biosynthesis, phytoalexin synthesis, oxidative burst, wax biosynthesis, while two down-regulated unigenes encoding leucine-rich repeat receptor protein kinase and subtilisin-like protease might be important for host-derived signal perception to AG1 IA strain invasion. According to Pathogen Host Interaction (PHI) database annotation, 1508 unigenes of AG1 IA strain were predicted and classified into 37 known pathogen species, in addition, unigenes encoding virulence, signaling, host stress tolerance, and potential effector were also predicted. This research uncovered transcriptional profiling during the early phase interaction between R. solani AG1 IA strain and Z. japonica, and will greatly help identify key pathogenicity of AG1 IA strain.

Cross-tolerance to biotic and abiotic stresses in plants: a focus on resistance to aphid infestation

Plants co-evolved with an enormous variety of microbial pathogens and insect herbivores under daily and seasonal variations in abiotic environmental conditions. Hence, plant cells display a high capacity to respond to diverse stresses through a flexible and finely balanced response network that involves components such as reduction-oxidation (redox) signalling pathways, stress hormones and growth regulators, as well as calcium and protein kinase cascades. Biotic and abiotic stress responses use common signals, pathways and triggers leading to cross-tolerance phenomena, whereby exposure to one type of stress can activate plant responses that facilitate tolerance to several different types of stress. While the acclimation mechanisms and adaptive responses that facilitate responses to single biotic and abiotic stresses have been extensively characterized, relatively little information is available on the dynamic aspects of combined biotic/abiotic stress response. In this review, we consider how the abiotic environment influences plant responses to attack by phloem-feeding aphids. Unravelling the signalling cascades that underpin cross-tolerance to biotic and abiotic stresses will allow the identification of new targets for increasing environmental resilience in crops.

Mitogen-activated protein kinase 6 mediates nuclear translocation of ORE3 to promote ORE9 gene expression in methyl jasmonate-induced leaf senescence

Methyl jasmonate (MeJA) is a potent promoter of plant senescence. ORESARA3 (ORE3)/ETHYLENE INSENSITIVE2 (EIN2), a protein similar to the members of the disease-related Nramp metal transporter family, is involved in cross-talk among several senescence processes related to abscisic acid, ethylene, MeJA, age and darkness. Nevertheless, the mechanism involved in the regulation of ORE3/EIN2 in exogenous MeJA-induced leaf senescence remains unclear. The C-terminal end of ORE3/EIN2 (CEND) was cleaved from ORE3/EIN2 located in the endoplasmic reticulum and then transferred to the nucleus during MeJA-induced senescence. Further analyses showed that mitogen-activated protein kinase 6 (MPK6) promoted CEND cleavage and nuclear translocation. Nuclear CEND accumulated ETHYLENE INSENSITIVE3 (EIN3), a transcription factor that accelerates MeJA-induced leaf senescence wherein ORESARA9 (ORE9) expression was suppressed in ein3, ore3, and mpk6 mutant plants. ChIP experiments revealed that EIN3 bound directly to the ORE9 promoter and this binding was enhanced in MeJA-induced leaf senescence. This study revealed the effect of the signalling pathway involving MPK6-ORE3-EIN3-ORE9 on regulating leaf senescence and provided insights into the mechanism of MeJA in promoting leaf senescence in Arabidopsis thaliana.

LSD1 and HY5 antagonistically regulate red light induced-programmed cell death in Arabidopsis

Programmed cell death (PCD) in plant is triggered by abiotic and biotic stress. Light-dependent PCD is unique to plants. Light-induced PCD also requires reactive oxygen species (ROS) and salicylic acid (SA). In this study, lesion simulating disease1 (LSD1) and elongated hypocotyl 5 (HY5) perform opposite roles to regulate excess red light (RL)-triggered PCD associated with ROS and SA production. Under RL, the lsd1 mutant released more ROS and SA and displayed a stronger cell death rate than the hy5 mutant. It was shown that active LSD1 converted into inactive form by changing the redox status of the plastoquinone pool, and HY5 interacted with phytochrome B (phyB) to promote PCD in response to RL. LSD1 inhibited the enhanced disease susceptibility 1 (EDS1) expression by upregulating SR1, whereas HY5 enhanced the enhanced EDS1 expression by binding to the G-box of the EDS1 promoter. This study suggested that LSD1 and HY5 antagonistically modulated EDS1-dependent ROS and SA signaling; thus, PCD was mediated in response to RL.

ROS-mediated enhanced transcription of CYP38 promotes the plant tolerance to high light stress by suppressing GTPase activation of PsbO2

As a member of the Immunophilin family, cyclophilin38 (CYP38) is discovered to be localized in the thylakoid lumen, and is reported to be a participant in the function regulation of thylakoid membrane protein. However, the molecule mechanisms remain unclear. We found that, CYP38 plays an important role in the process of regulating and protecting the plant to resist high light (HL) stress. Under HL condition, the gene expression of CYP38 is enhanced, and if CYP38 gene is deficient, photochemistry efficiency, and chlorophyll content falls distinctly, and excessive reactive oxygen species synthesis occurs in the chloroplast. Western blot results showed that the D1 degradation rate of cyp38 mutant plants is faster than that of wide type plants. Interestingly, both gene expression and activity of PsbO2 were drastically enhanced in cyp38 mutant plants and less changed when the deleted gene of CYP38 was restored under HL treatment. This indicates that CYP38 may impose a negative regulation effect on PsbO2, which exerts a positive regulation effect in facilitating the dephosphorylation and subsequent degradation of D1. It is also found that, under HL condition, the cytoplasmic calcium ([Ca(2+)]cyt) concentration and the gene expression level of calmodulin 3 (CaM3) arose markedly, which occurs upstream of CYP38 gene expression. In conclusion, our results indicate that CYP38 plays an important role in plant strengthening HL resistibility, which provides a new insight in the research of mechanisms of CYP38 protein in plants.