Abiotic and Biotic Stresses and Changes in the Lignin Content and Composition in Plants

Lignin is a polymer of phenylpropanoid compounds formed through a complex biosynthesis route, represented by a metabolic grid for which most of the genes involved have been sequenced in several plants, mainly in the model-plants Arabidopsis thaliana and Populus. Plants are exposed to different stresses, which may change lignin content and composition. In many cases, particularly for plant-microbe interactions, this has been suggested as defence responses of plants to the stress. Thus, understanding how a stressor modulates expression of the genes related with lignin biosynthesis may allow us to develop study-models to increase our knowledge on the metabolic control of lignin deposition in the cell wall. This review focuses on recent literature reporting on the main types of abiotic and biotic stresses that alter the biosynthesis of lignin in plants.

Villin Family Members Associated with Multiple Stress Responses in Cotton

Villin(VLN)is considered to be one of the most important actin-binding proteins,participates in modulating the actin cytoskeleton dynamics,plays essential role in plant development and resisting adverse environments.However,systematic studies of the VLN gene family have not been reported in cotton(Gossypium).In this study,14 GhVLNs were identified in G.hirsutum.These GhVLN genes were distributed in 6 A-subgenome chromosomes and 6 D-subgenome chromosomes of the allotetraploid upland cotton and classified into three phylogenetical groups based on the classification model of AtVLNs.In addition,the 14 GhVLN genes have highly conserved gene structure and motif architecture.The number of introns was ranged from 18 to 22 and the length of protein sequences was varied from 901 to 1077.Six gelsolin homology domains,G1–G6,and villin headpiece domain,VHP,were existed in all GhVLNs with the exception of two VLNs(GhVLN6 and GhVLN13)which lacked VHP.Cis-elements analysis revealed that the promoter regions of GhVLNs contained various light related components and also elements responsible for phytohormones and stresses response,indicating that,when subjected to those adverse environments,cotton plants may activate the response system by targeting VLN genes to survive the crisis.Heatmaps showed that the GhVLN genes exhibited various expression patterns,some were accumulated in certain tissues,root,petal,stamen or elongating fibers,and some were obviously induced by environmental changes.Especially GhVLN3 and GhVLN10 were highly and preferentially expressed in elongating fibers and distinctly upregulated by abiotic(salt,PEG,cold and heat)and biotic(Verticillium dahliae V991)stresses.This study may provide useful information for biological function identification of GhVLN genes and gene resources for creating high-quality and various resistant cotton germplasms.

Genetic and Epigenetic Effects of Plant-Pathogen Interactions： An Evolutionary Perspective

Recent reports suggest that exposure to stress is capable of influencing the frequency and pattern of inherited changes in various parts of the genome. In this review, we will discuss the influence of viral pathogens on somatic and meiotic genome stability of Nicotiana tabacum and Arabidopsis thaliana. Plants infected with a compatible pathogen generate a systemic recombination signal that precedes the spread of pathogens and results in changes in the somatic and meiotic recombination frequency. The progeny of infected plants exhibit changes in global and locusspecific DNA methylation patterns, genomic rearrangements at transgenic reporter loci and resistance gene-like-loci, and even tolerance to pathogen infection and abiotic stress. Here, we will discuss the contribution of environmental stresses to genome evolution and will focus on the role of heritable epigenetic changes in response to pathogen infection.

High REDOX RESPONSIVE TRANSCRIPTION FACTOR1 Levels Result in Accumulation of Reactive Oxygen Species in Arabidopsis thaliana Shoots and Roots

Redox Responsive Transcription Factor1 （RRTF1） in Arabidopsis is rapidly and transiently upregulated by H202, as well as biotic- and abiotic-induced redox signals. RRTF1 is highly conserved in angio- sperms, but its physiological role remains elusive. Here we show that inactivation of RRTF1 restricts and overexpression promotes reactive oxygen species （ROS） accumulation in response to stress. Transgenic lines overexpressing RRTF1 are impaired in root and shoot development, light sensitive, and susceptible to Alternaria brassicae infection. These symptoms are diminished by the beneficial root endophyte Piriformospora indica, which reduces ROS accumulation locally in roots and systemi- cally in shoots, and by antioxidants and ROS inhibitors that scavenge ROS. More than 800 genes were detected in mature leaves and seedlings of transgenic lines overexpressing RRTF1; ∽40% of them have stress-, redox-, ROS-regulated-, ROS-scavenging-, defense-, cell death- and related functions. Bioinformatic analyses and in vitro DNA binding assays demonstrate that RRTF1 binds to GCC-box-like sequences in the promoter of RRTFl-responsive genes. Upregulation of RRTF1 by stress stimuli and H202 requires WRKY18/40/60. RRTF1 is co-regulated with the phylogenet- ically related RAP2.6, which contains a GCC-box-like sequence in its promoter, but transgenic lines overexpressing RAP2.6 do not accumulate higher ROS levels. RRTF1 also stimulates systemic ROS accumulation in distal non-stressed leaves. We conclude that the elevated levels of the highly conserved RRTF1 induce ROS accumulation in response to ROS and ROS-producing abiotic and biotic stress signals.

Molecular basis for optimizing sugar metabolism and transport during fruit development

Sugars are fundamental metabolites synthesized in leaves and further delivered to fruit in fruit crops.They not only provide"sweetness"as fruit quality traits,but also function as signaling molecules to modulate the responses of fruit to environmental stimuli.Therefore,the understanding to the molec-ular basis for sugar metabolism and transport is crucial for improving fruit quality and dissecting responses to abiotic/biotic factors.Here,we provide a review for mol ecular components involved in sugar metabolism and transport,crostalk with hormone signaling and the roles of sugars in responses to abiotic and biotic stresses.Moreover,we also envisage the strategies for optimizing sugar metabolism during fruit quality maintenance.

Plant target of rapamycin signaling network:Complexes,conservations,and specificities

Target of rapamycin(TOR)is an evolutionarily conserved protein kinase that functions as a central signaling hub to integrate diverse internal and external cues to precisely orchestrate cellular and organismal physiology.During evolution,TOR both maintains the highly conserved TOR complex compositions,and cellular and molecular functions,but also evolves distinctive roles and strategies to modulate cell growth,proliferation,metabolism,survival,and stress responses in eukaryotes.Here,we review recent discoveries on the plant TOR signaling network.We present an overview of plant TOR complexes,analyze the signaling landscape of the plant TOR signaling network from the upstream signals that regulate plant TOR activation to the downstream effectors involved in various biological processes,and compare their conservation and specificities within different biological contexts.Finally,we summarize the impact of dysregulation of TOR signaling on every stage of plant growth and development,from embryogenesis and seedling growth,to flowering and senescence.

Transcriptional Repression by Histone Deacetylases in Plants

Reversible histone acetylation and deacetylation at the N-terminus of histone tails play crucial roles in regulation of eukaryotic gene activity. Acetylation of core histones usually induces an ＇open＇ chromatin structure and is associated with gene activation, whereas deacetylation of histone is often correlated with ＇closed＇ chromatin and gene repression. Histone deacetylation is catalyzed by histone deacetylases （HDACs）. A growing number of studies have demonstrated the importance of histone deacetylation/acetylation on genome stability, transcriptional regulation, and development in plants. Furthermore, HDACs were shown to interact with various chromatin remolding factors and transcription factors involved in transcriptional repression in multiple developmental processes. In this review, we summarized recent findings on the transcriptional repression mediated by HDACs in plants.