The Molecular Mechanism Analysis Of Response To Drought And Salt Stresses In Rapeseed(Brassica Napus L.)seedling Stage By Transcriptome

The increasing shortage of water resources is a common problem faced by global agriculture.Drought has become a limiting factor limiting crop productivity,ranking first of all the natural disasters.The response and resistance(tolerance)mechanisms of crops under salt stress are the same or similar to drought stress in many aspects.At present,the annual planting area and yield of rapeseed in China account for one quarter of the world,and it is the main rapeseed producing area in the world.The research on the mechanism of salt tolerance and drought resistance of rapeseed is an important part of crop stress resistance research.Although scholars have made great progress in understanding the mechanism of salt tolerance and drought resistance at various levels(physiological,molecular,etc.),the molecular mechanism of salt tolerance and drought stress is not clear enough,so it still needs to be further explored.Based on previous studies on the mechanism of the response of rapeseed to drought stress and salt stress,we focused on exploring the changes of lnc RNAs(Long noncoding RNAs)of rapeseed in response to drought stress from the omics perspective and the molecular mechanism of melatonin-induced improvement of the tolerance of rapeseed to salt stress.The main results were as follows:(1)In the early stage,drought-resistant(Q2)and drought-sensitive(Qinyou8)rapeseed lines were obtained through identification.We used next-generation sequencing technology to obtain lnc RNAs data from leaves of two different genotypes of rapeseed under drought stress and re-watering.369 down-regulated and 108 up-regulated lnc RNAs were detected in Q2 compared with 449 and 257 in Qinyou8,respectively.Lnc RNA-m RNA interaction network analysis indicated that the co-expression network of Q2 was composed of 145 network nodes and 5,175 connections,while the co-expression network of Qinyou8 was composed of 305 network nodes and 22,327 connections.We further identified 34 transcription factors(TFs)corresponding to 126 differentially expressed lnc RNAs in Q2,and 45 TFs corresponding to 359 differentially expressed lnc RNAs in Qinyou8.Differential expression analysis of lnc RNAs indicated that up-and down-regulated m RNAs co-expressed with lnc RNAs participated in different metabolic pathways and were involved in different regulatory mechanisms in the two genotypes.Lnc RNAs may be involved in plant hormone signaling and defense/stress response by regulating co-expressed and co-located m RNAs in response to drought stress and rehydration.This study deepened our understanding of the expression characteristics of lnc RNAs in rapeseed under drought stress and rehydration,and provided ideas for further studying the function and mechanism of specific lnc RNAs in rapeseed in response to drought stress.(2)Previous studies have found that the salt tolerance of rapeseed could be improved by appropriate amount of melatonin.In this study,the contents of different hormones in leaves were measured under control(CK),salt(ST)and melatonin plus salt(MS)treatments.At the same time,next-generation sequencing technology was used to obtain the transcriptome data of leaves and roots under control(CK),salt(ST)and melatonin plus salt(MS)treatments.By comparing the gene expression of MS and ST in leaves and roots,the differentially expressed genes(DEGs)were screened out.Kyoto Encyclopedia of Genes and Genomes(KEGG)enrichment analyses highlighted the significant pathways,which were mainly related to plant hormone synthesis and signal transduction,lignin and fatty acid metabolism.The important functional genes in the target KEGG pathways were identified.Furthermore,some members of transcription factor family also participated in the response process.Combined with the analysis of hormone(campesterol,jasmonic acid,and gibberellic acid 3)content in the seedlings,it was found that melatonin could induce the changes of endogenous hormone metabolism network,which promoted seedling growth.This study identified the biological pathways and candidate genes that play an important role in the interaction process of melatonin and salt stress,which laid a foundation for further revealing the mechanism of melatonin improving the salt tolerance of crops.