miR398b negatively regulates cotton immune responses to Verticillium dahliae via multiple targets

MicroRNAs(miRNAs)play essential roles in plant defense responses,although such roles have not been identified in cotton in response to the plant pathogenic fungus Verticillium dahliae.In this study,the functions of miR398b and its target genes in cotton-V.dahliae interaction were investigated.The transcript levels of miR398b were down-regulated by V.dahliae infection and miR398b overexpression in cotton made the plants more susceptible to V.dahliae.The results suggest that miR398b negatively regulates cotton resistance to V.dahliae.This may occur by miR398b repression of some CC-NBS-LRR genes via translational inhibition,interfering with defense responses and leading to cotton susceptibility to V.dahliae.Alternatively,miR398b may guide the cleavage of the mRNAs of GhCSD1,GhCSD2 and GhCCS,each of which functions in reactive oxygen species(ROS)regulation and homeostasis,thereby causing excessive ROS accumulation in miR398b-overexpressing plants in response to V.dahliae infection.This study suggests conserved and novel roles of miR398b in the cotton–V.dahliae interaction.These discoveries may be coupled with new strategies in cotton breeding programs to improve resistance to V.dahliae.

Heme Oxygenase-1 is Associated with Wheat Salinity Acclimation by Modulating Reactive Oxygen Species Homeostasis

Heme oxygenase-1 （HO-1） has been recently identified as an endogenous signaling system in animals. In this study, HO-1 upregulation and its role in acquired salt tolerance （salinity acclimation） were investigated in wheat plants. We discovered that pretreatment with a low concentration of NaCl （25 mmol/L） not only led to the induction of HO-1 protein and gene expression, as well as enhanced HO activity, but also to a salinity acclimatory response thereafter. The effect is specific for HO-1, since the potent HO-1 inhibitor zinc protoporphyrin IX blocks the above cytoprotective actions, and the cytotoxic responses conferred by 200 mmol/L NaCl are reversed partially when HO-1 inducer hemin is added. Heme oxygenase catalytic product, carbon monoxide （CO） aqueous solution pretreatment, mimicked the salinity acclimatory responses. Meanwhile, the CO-triggered re-establishment of reactive oxygen species （ROS） homeostasis was mainly guaranteed by the induction of total and isozymatic activities, or corresponding transcripts of superoxide dismutase, ascorbate peroxidase, and cytosolic peroxidase （POD）, as well as the downregulation of NADPH oxidase expression and cell-wall POD activity. A requirement of hydrogen peroxide homeostasis for HO-1-mediated salinity acclimation was also discovered. Taken together, the above results suggest that the upregulation of HO-1 expression was responsible for the observed salinity acclimation through the regulation of ROS homeostasis.

Systematic analysis and functional verification of citrus glutathione S-transferases reveals that CsGSTF1 and CsGSTU18contribute negatively to citrus bacterial canker

Citrus bacterial canker(CBC) is resulted from Xanthomonas citri subsp. citri(Xcc) infection and poses a significant threat to citrus production.Glutathione S-transferases(GSTs) are critical in maintaining redox homeostasis in plants, especially in relation to abiotic and biotic stress responses. However, the function of GSTs in resisting CBC remains unclear. Here, citrus glutathione S-transferases were investigated applying a genome-wide approach. In total, 69 CsGSTs belonging to seven classes were identified, and the phylogeny, chromosomal distribution, gene structures and conserved motifs were analyzed. Several CsGSTs responded to Xcc infection, as observed in the upregulation of CsGSTF1 and CsGSTU18 in the CBC-sensitive ‘Wanjincheng' variety but not in the resistant ‘Kumquat' variety. CsGSTF1 and CsGSTU18 were localized at the cytoplasm. Transient overexpression of CsGSTF1 and CsGSTU18 mediated reactive oxygen species(ROS) scavenging, whereas the virus-induced gene silencing(VIGS) of CsGSTF1 and CsGSTU18 caused strong CBC resistance and ROS burst. The present study investigated the characterization of citrus GST gene family, and discovered that CsGSTF1 and CsGSTU18 negatively contributed to CBC through modulating ROS homeostasis. These findings emphasize the significance of GSTs in infection resistance in plants.

Allene oxide synthase 1 contributes to limiting grain arsenic accumulation and seedling detoxification in rice

Arsenic(As)is a cancerogenic metalloid ubiquitously distributed in the environment,which can be easily accumulated in food crops like rice.Jasmonic acid(JA)and its derivatives play critical roles in plant growth and stress response.However,the role of endogenous JA in As accumulation and detoxification is still poorly understood.In this study,we found that JA biosynthesis enzymes Allene Oxide Synthases,OsAOS1 and OsAOS2,regulate As accumulation and As tolerance in rice.Evolutionary bioinformatic analysis indicated that AOS1 and AOS2 have evolved from streptophyte algae(e.g.the basal lineage Klebsormidium flaccidum)-sister clade of land plants.Compared to other two AOSs,OsAOS1 and OsAOS2 were highly expressed in all examined rice tissues and their transcripts were highly induced by As in root and shoot.Loss-of-function of OsAOS1(osaos1-1)showed elevated As concentration in grains,which was likely attributed to the increased As translocation from root to shoot when the plants were subjected to arsenate[As(Ⅴ)]but not arsenite[As(Ⅲ)].However,the mutation of OsAOS2(osaos2-1)showed no such effect.Moreover,osaos1-1 and osaos2-1 increased the sensitivity of rice plants to both As(Ⅴ)and As(Ⅲ).Disrupted expression of genes involved in As accumulation and detoxification,such as OsPT4,OsNIP3;2,and OsOASTL-A1,was observed in both osaos1-1 and osaos2-1 mutant lines.In addition,a As(Ⅴ)-induced significant decrease in Reactive Oxygen Species(ROS)production was observed in the root of osaos1-1 but not in osaos2-1.Taken together,our results indicate OsAOS1 modulates both As allocation and detoxification,which could be partially attributed to the altered gene expression profiling and ROS homeostasis in rice while OsAOS2 is important for As tolerance.