Molecular Mechanism Analysis Of Cotton In Response To Salt Stress

Cotton（Gossypium）is the most important fiber cash crop.China is the largest producer and consumer of cotton in the world.Nowadays,soil salt stress becomes a key limiting factor restricting cotton production in China.It is very important to improve salt tolerance on the basis of ensuring high yield and quality for cotton.Transcriptomics and proteomics played important roles in the analysis of important biological processes in plants,and explored important hormone signal transduction pathways involved in plant stress response,such as jasmonic acid（JA）,which was involved in the regulation of plant resistance to salt stress.However,the mechanism of JA signal transduction and the relationship between JA and salt tolerance in cotton are not clear.In this study,the mechanism of cotton response to salt stress was investigated by integrated transcriptome and proteome analysis.And some candidate genes were identified.Moreover,a genome-wide screen and analysis for JAZ genes in cotton genome,and functions in regulating JA signal and salt stress were also studied.The results of this study are as follows:1.Identification of candidate genes involved in salt stress response in cotton by integrated transcriptome and proteome analysisThrough transcriptome analysis of leaves treated with salt stress for 0 h（T0）,3 h（T3）and12 h（T12）,we identified 8,436,11,628 and 6,311 DEGs in T0-T3,T0-T12 and T3-T12,respectively.These DEGs were mainly enriched in 16 pathways,including metabolic pathways,biosynthesis of secondary metabolites,starch and sucrose metabolism,carbon metabolism and plant-pathogen interaction.Plant hormone signals,protein kinases and transcription factors were also widely involved in salt stress response in cotton.A total of459 DEPs were identified by proteomic analysis,of which 273,99 and 260 were identified in T0-T3,T0-T12 and T3-T12,respectively.These DEPs were mainly enriched in metabolic pathways,biosynthesis of secondary metabolites,photosynthesis,pyruvate metabolism and other pathways.Through the association analysis of transcriptome and proteome,there were 77,70 and47 associated DEGs and DEPs were enriched in T0-T3,T0-T12 and T3-T12,respectively.These genes/proteins were mainly enriched in metabolic pathways,biosynthesis of secondary metabolites,ribosome,photosynthesis and biosynthesis of amino acids.We identified 12 candidate genes,such as GhLEA14（Gh_A11G0835）、GhKCS6（Gh_A03G1286）、GhLOX2（Gh_D05G0683）、GhPRXR1（Gh_A05G1452）、GhPIP2（Gh_D09G1409）、GhPOD（Gh_A08G0714）、GhFIB（Gh_A05G1494）、GhALDH7B4（Gh_D06G1578）、GhUSP（Gh_A03G0386）、GhAVP1（Gh_D05G0122）、GhADH1（Gh_A01G1605）and GhNCL（Gh_A11G2591）,might play an important role in cotton response to salt stress.2.Identification and analysis of JAZ family genes in cottonIn the present study,13,15,25 and 30 JAZ genes were identified in Gossypium arboreum,Gossypium raimondii,Gossypium barbadense and Gossypium hirsutum,respectively.All the cotton JAZ proteins could be clustered into six groups（I–VI）,variation analysis showed that the SNP density of GhJAZ genes in wild species was much higher than that in domesticated species.Ka/Ks analysis revealed that purifying selection of JAZ genes occurred in both diploid and polyploid cotton species.Yeast two-hybrid（Y2H）experiments showed extensive interactions among GhJAZ proteins,including homo-and heteromeric interactions.GhJAZ proteins can interact with MYC transcription factors GhMYC2 and GhMYC2a,and repress the transcriptional activation activity of MYC transcription factors.In addition,GhNINJA can interact with multiple GhJAZ proteins.Tissue expression pattern analysis showed that all the GhJAZ genes were expressed at least in one tissue,and 13 genes were expressed in all tissues,nine genes were highly expressed in the root and 13 genes were highly expressed in the stem.Stress induced expression pattern analysis showed that all the genes exhibited altered expressions in response to one or more stress factors,heat and salinity stresses induced relatively more fluctuations in the transcript abundance of GhJAZ genes than the cold and PEG stresses.In addition,GhJAZ genes were also involved in the response to jasmonate acid（JA）,abscisic acid（ABA）and hydrogen peroxide（H₂O₂）.3.Overexpression of GhJAZ2 represses JA signal and significantly reduces the tolerance to salt stress of cottonThrough transcriptome analysis,a total of 273 DEGs were identified between the control（YZ1）and the transgenic overexpression line（J39）.There were 204 genes showed down-regulated and 69 genes showed up-regulated expression patterns in the overexpression line.These DEGs were significantly enriched in“Metabolic pathway”,“Plant-pathogen interaction”and“Plant hormone signal transduction”.Among 273 DEGs,92 genes were involved in MeJA-induced differential expression.Most of the genes involved in JA synthesis and signal transduction,such as GhLOX2,GhAOC,GhAOS,GhJAZ3 and GhbHLH,were significantly repressed in overexpression cotton plants.The regulation of MYC transcription factors by GhJAZ2 might be one of the important factors for the inhibition of JA signal in GhJAZ2 overexpression plants.Through phenotypic identification under salt stress treatments,we found overexpressing GhJAZ2 significantly decreased the tolerances to salt stress in cotton,but there was no significant difference between the control and GhJAZ2-RNAi plants.Salt stress induced the activation of JA signal,but this effect was blocked in overexpressing cotton plants.The inhibition of JA signal by GhJAZ2 might be an important factor for the salt sensitivity of overexpression cotton plants.In addition,GhJAZ2 might negatively regulate salt tolerance of cotton by inhibiting the expression of genes involved in JA independent signal,such as heavy metal transport/detoxification superfamily proteins,calmodulin binding proteins,transcription factors,senescence related genes.