Genome-wide Analysis Of The Expansin Gene Family In Phyllostachys Edulis And Functional Analysis Of PeEXPA8

Moso bamboo（Phyllostachys edulis）is the bamboo species with the largest area and the best economic benefits in China.In recent years,with the global warming and other environmental problems becoming more and more serious,moso bamboo is subjected to a variety of environmental stresses such as rain,snow and freezing,which have seriously affected the growth of moso bamboo.The morphogenesis and organ development of moso bamboo are inseparable from the expansins that regulate cell wall relaxation and elongation.Therefore,study on the molecular characteristics and expression patterns of PeEXPs under stress conditions is of great significance for revealing the molecular mechanism of bamboo resistance.In this study,based on the comprehensive analysis of expansins in moso bamboo,PeEXPA8 was cloned and its function was validated by transgenic means.The main results are as follows:（1）A total of 43 members of expansin family were identified in the genome of moso bamboo,which belonged to four subfamilies:EXPA,EXPB,EXLA and EXLB,distributed on 37 Scaffolds.There are some differences in the gene structure,the basic physicochemical properties,and the secondary and tertiary protein structure,but the similarity of the members in each subfamily indicates they are relatively conservative in evolution.Most members of PeEXPs have 1 to 5 introns,among which PeEXPAs are more likely to be 2,PeEXPBs is more likely to be 3,and PeEXLAs and PeEXLB are more likely to be 4.All amino acids encoded by PeEXPs have high frequency codons,most of the proteins are alkaline hydrophilic proteins.（2）Based on the transcriptome data analysis of different tissues of moso bamboo,there were differences in the expression abundance of PeEXPs in different tissues and different developmental stages of moso bamboo.The results of q RT-PCR further showed that PeEXPAs are expressed differently in different tissues.Most genes are expressed at the highest level in leaves,indicating that they may play an important role in the growth of leaves.In addition,the quantitative analysis of PeEXPA8 showed that PeEXPA8 was mainly expressed in bamboo leaves,rhizomes,rhizome buds and roots.The quantitative results were consistent with the prediction of heat map.With the increase of shoot height,the expression of PeEXPA8 was up-regulated continuously,and the expression in the lower part of the shoot was always higher than that in the upper part of the shoot.The promoter region of PeEXPA8was cloned,which is 1 655 bp.Plant CARE element analysis found that the promoter region of PeEXPs contains many hormone response elements and stress response elements.The results of q RT-PCR showed that PeEXPA2 responded to low temperature,drought and ABA,GA,IAA hormones in varying degrees,while PeEXPA8 responded to ABA,IAA and low temperature stress.（3）PeEXPA8 was heterologously transformed into rice（Oryza sativa）and square bamboo（Chimonobambusa quadrangularis（Fenzi）Makino）and the growth and development phenotypes of T₁ generation transgenic rice were observed and recorded that the overexpression of PeEXPA8 increased plant height,leaf area and stem width of transgenic rice,but the tiller was inhibited.Meawhile,the glume cells and the papillae on the leaf surface of transgenic rice were elongated,and the grains were enlarged.After stress treatment,it was found that after high salt（150 m M Na Cl）and hormone（1μL,3μL ABA）treatment,transgenic rice lines performed better and had more and longer roots as well as physiological indexes such as malonaldehyde,catalase,superoxide dismutase content and DAB and NBT staining,which indicated that overexpression of PeEXPA8 improved the stress resistance of transgenic rice.This study comprehensively analyzed the basic characteristics of the members of the moso bamboo expansin family.And it is preliminarily proved that PeEXPA8 can not only affect the plant type of rice,but also has a certain effect on improving the stress resistance of rice.These results provide a reference for further study on the functions of the members of moso bamboo expansin.