The Role Of MYB51 In The Defense Response And Mucilage Secretion Of Arabidopsis

Glucosinolates are important secondary metabolites in Cruciferae.Indole glucosinolates derived from tryptophan play an important role in the resistance and defense of Arabidopsis.It can not only restrict the growth of pathogenic bacteria directly through the antibacterial activity of its degradation products,but also act as a signal molecule to trigger highly conserved immune response in plant.For example,in Arabidopsis,the degradation products of indole glucosinolates are involved in the accumulation of callose in cell wall,programmed cell death and systemic acquired resistance induced by pathogens.In addition,indole glucosinolates and IAA have common synthetic precursors,and their metabolic processes are closely related to the synthesis of IAA.Therefore,indole glucosinolates may play an important role in plant growth and development,but at present,people's cognition on this aspect is very limited.In view of the diversity and complexity of the role of indole glucosinolates in disease resistance and defense response,and the limitations of people's cognition on its role in growth and development,it is of great significance to conduct in-depth and systematic research on the physiological function of indole glucosinolates.MYB51 is an important transcription factor regulating the synthesis of indole glucosinolates.In this study,MYB51 gene deletion mutant was used as the material,flg22(22 amino acid peptides from bacterial flagellin,a conservative structure that can induce plant immune response)is the inducer of defense response.The transcriptome of wild-type Arabidopsis and myb51 Arabidopsis before and after flg22 treatment were compared and analyzed,and the role of MYB51 in disease resistance and defense response and growth and development was newly recognized.The main research results are in two aspects:1.Although myb51 has no significant morphological phenotype under non stress conditions,the analysis of transcriptome data shows that MYB51 has a profound influence on many biological processes under normal growth conditions,especially on the development of cell wall.Based on the analysis of differentially expressed genes,we studied the process of mucilage secretion in testa: 1)The absence of indole glucosinolates can affect the development of mucilage secretory cells in seed coat,change the structure of seed epidermis,and cause the defect of mucilage secretion in seed coat;2)The absence of aliphatic glucosinolates also cause the changes of testa structure and the defects of mucilage secretion,which indicates that both glucosinolates with different side chain structures are involved in the regulation of mucilage secretion in testa,so this regulation may depend on the core structure of glucosinolates;3)Quantitative Real time PCR analysis of the key node genes in the mucilage secretion regulatory network of testa showed that:the expression of the coding genes of ?-L-arabinofurosidase BXL1 and peroxidase PRX36 in the glucosinolatesdeletion mutant decreased significantly,and both of them played important roles in the development of mucilage secretory cells and mucilage formation in testa.Therefore,glucosinolates may be involved in the process of seed coat mucilage secretion by regulating the expression of these two enzymes.2.Comparative analysis of flg22 response genes between myb51 and wild type Arabidopsis,the results show that: 1)In addition to the known mechanism of MYB51,MYB51 may be involved in many other pathogen defense processes,including pathogen recognition,signal transduction and PR protein activation;2)Some members of WRKY family,such as WRKY33 and WRKY40,play an important regulatory role in plant disease resistance immune response.They can directly act on the upstream of MYB51 promoter and regulate the synthesis of indole glucosinolates.In the wild type,WRKY33 and WRKY40 are the hub genes of many flg22 response genes,In myb51,the response to flg22 is defective and no longer hub genes.This shows that MYB51 has a positive feedback effect on WRKY;3)Ethylene(ET)is an important hormone in plant immune response.Under the action of pathogen,ET signaling pathway can induce the expression of MYB51,promote the synthesis of indole glucosinolates,thus activate the callose accumulation process of cell wall,which is an important regulatory factor in the upstream of MYB51.Similar to WRKY,the response of some important transcription factors in ET pathway to flg22 is also dependent on MYB51.It shows that MYB51 also has a positive feedback regulation effect on the ET signal pathway upstream.It can be seen that MYB51 has a positive feedback effect on its upstream regulatory factors,so it can indirectly affect more defense processes.