Genome-wide Identification And Transcriptomic Analysis Of PMEI And XTH Family Genes In Brassica Napus

Boron(B)is an essential microelement for the growth and development of higher plants.According to previous studies,the response of plants to boron deficiency stress is related to the cell wall.Boron mainly combines with rhamnogalacturonan Ⅱ in the cell walls of plants.Brassica napus L.is an important oil crop and has a high demand for boron.When boron deficiency occurs,its growth and development,especially its reproductive development,are seriously affected,and the cell wall components in flower organs change.It has been reported that xyloglucan endotransglycosylase/hydrolase(XTH)and pectin methylesterase inhibitor(PMEI)in primary cell wall play an important role in stress resistance,floral organ development and fertility of plants.Previous studies on the response of Arabidopsis and B.napus seedlings to boron deficiency stress found that these genes responded to boron deficiency stress.In this study,we identified all the members of these families from the genome of Brassica napus,analyzed and predicted the properties of their genes and gene products,and analyzed their phylogenetic relationships.At the same time,the transcriptional profiles of flower buds under long-term boron deficiency stress were analyzed by using boron efficient cultivar Zhongshuang 11(ZS11)and boron inefficient cultivar Wester10(W10).The transcriptional responses of BnaXTH and BnaPMEI in flower buds to boron deficiency stress were analyzed,and the key genes in the response process of boron deficiency in flower bud cell wall were screened by co expression network analysis.The main results are as follows:(1)163 PMEI genes and 94 XTH genes were identified from B.napus cv.Darmorbzh genome.According to the phylogenetic distance,the BnaPMEI gene family was divided into seven clades,and the BnaXTH gene family was divided into four clades.The sequence analysis of the two gene families was carried out to predict their gene structure,protein domain and basic protein properties.The phylogenetic process of the two gene families in Brassica was analyzed with the genomes of Arabidopsis thaliana,Brassica rapa and Brassica oleracea,and then the two gene families were expanded by both genome-wide duplication and tandem replication.The results showed that the non-synonymous mutation rate of most members was less than the synonymous mutation rate,indicating that the two cell wall polysaccharides related gene families play a basic and conservative role in the growth and development process of B.napus.(2)The differentially expressed genes in flower buds of B-efficient cultivar ZS 11 and B-inefficient cultivar W10 were analyzed under long-term boron deficiency stress and normal boron treatment.The co-expression relationship of BnaPMEI and BnaXTH in response to boron deficiency were analysed,and three hub genes BnaC09.XTH9,BnaCnn.XTH16 and BnaC09.PMEI3 were predicted.BnaXTH9 subfamily and BnaXTH3 subfamily genes are specifically expressed in reproductive organs,which may play an important role in the structural changes of flower buds cell walls and the development of flower under boron deficiency stress.Co-expression network analysis showed that the changes of cell wall polysaccharide in flower buds under boron deficiency stress may be related to sugar metabolism enzymes,membrane lipid metabolism and peroxidation related genes.(3)Exploring the analysis assay for RG-Ⅱ dimerization determination with PAGE and HPLC,which provided technical support for building a more convenient RG-Ⅱ determination platform for boron nutrition study in B.napus.In conclusion,all of the BnaPMEI and BnaXTH family genes were systematically identified and analyzed,and the hub genes of the two gene families in response to boron deficiency in rapeseed flower buds were obtained,which provided reference information for the study of boron deficiency responses in the cell walls of B.napus.