Identification Of CircRNAs And Their Responses To Abiotic Stress In Brassica Napus L.

Circular RNA?circ RNA?is a type of covalently-bonded single-stranded circular RNA molecule that exists widely in animals and plants.Previous studies have shown that circ RNAs can act as a mi RNA sponge to regulate the expression of target genes,participate in the transcriptional regulation of parental genes,and interact with RNA binding proteins.At present,only 16 species of plants'circ RNAs have been identified,but it does not include rapeseed?Brassica napus L.?.Related studies have revealed that circ RNAs in corn can directly participate in the response to drought stress.Therefore,the identification of circ RNAs in rapeseed and the analysis of their response to abiotic stress will further enrich the biological function of circ RNA.Besides,it provides new ideas and theoretical basis for the genetic improvement of crop resistance,and provides potential molecular markers for rapeseed resistance breeding.In this study,seedlings of rapeseed“ZS11”were cultured in 20%PEG6000 solution,300 mmol.l^-1 Nacl solution and 4 ^oC/2 ^oC diurnal temperature environment in groups,to simulate drought stress,salt stress and low temperature stress environment respectively.Then we extracted leaf tissue for circ RNAs sequencing.On this basis,the molecular characteristics and distribution of circ RNAs were analyzed by bioinformatics,and the mechanism of rapeseed circ RNAs'responses to abiotic stress was studied.The main results are summarized as follows:1. Identification of circ RNAs and their characteristic distribution in rapeseed.A total of 1597 circ RNAs were identified in rapeseed.After analyzing their characteristic information,it was found that the quantity and expression abundance of circ RNAs were lower than those of model species;circ RNAs are mainly derived from the gene coding region,in which the number of introns and intergenic circ RNAs is significantly more than other species;the average length of circ RNAs is 731.19 nt,which is larger than most identified species,and the length of some intergenic circ RNAs exceeds 3000 nt;only 7.42%of the splicing sites can undergo alternative back-splicing,indicating that this phenomenon is not common in rapeseed;37.26%of circ RNAs in rapeseed are conserved among species,and this conservatism is closely related to the genetic relationship between species.2. Specificity of circ RNAs in abiotic stress.By comparing the characteristics of circ RNAs in the control group,drought stress group,low temperature stress group and salt stress group,it was found that the stress environment changed the number and expression abundance of circ RNAs,but it did not affect the distribution of the basic characteristics of circ RNAs.At the same time,it was found that low temperature stress could change the source type of circ RNAs in rapeseed,and the amount of circ RNAs derived from the gene coding region would increase with the occurrence of the low temperature stress.3. Construction of circ RNAs regulatory network in rapeseed.We found that a total of519 circ RNAs contain potential mi RNA target sites,which can bind to 92 mi RNAs.Among them,56 mi RNAs can find downstream target functional genes in the reference genome.According to the targeting relationship between them,the regulatory network of"circ RNA-mi RNA-m RNA"in rapeseed was constructed,and the regulatory network containing differentially expressed circ RNA was selected from them.We found that some of the differentially expressed circ RNAs can be combined with mi RNA families such as mi R169that are closely related to abiotic stresses,which initially indicates that circ RNAs in rapeseed may act as mi RNA sponges in response to abiotic stresses.4. The important biological process of circ RNAs regulate parental genes in response to abiotic stress.Through functional enrichment analysis of differentially expressed circ RNAs'parental genes,it is found that circ RNAs response to water depletion in drought stress group,response to salt and osmotic stress in salt stress group,and response to cold stress in low temperature stress group.At the same time,in both three types of abiotic stress,circ RNA can improve the plant's ability to perceive and resist the external environment by regulating stress-related secondary metabolites,signaling processes that mediate plant hormones and photosynthesis.