Study On Kinase Domain Of Arabidopsis Root Growth Factor Receptor 3 In Disease Resistance

In Arabidopsis thaliana,a set of cytoplasmic membrane located proteins are called receptor-like protein kinases(RLKs),which are similar to the structures of receptor protein kinases(RPK)in animals.After sensing the external signals,RLKs activate their kinase domain to transmit the signals into the cells and regulate many physiological reactions in plants,such as plant disease resistance,growth and development,hormone regulation,plant morphological changes,stress response,and so on.It is a key component in various signaling pathways.However,the role of each receptor-like protein kinases in various signaling pathways is not clear enough and has attracted much attention in this field.In order to identify RLKs involved in plant defense response,the extracellular domain of Arabidopsis EF-TU Receptor(EFR)receptor was fused with multiple kinase domains of LRR-RLK to form the recombinant LRR-RLKs expression cassette.Screening of recombinant LRR-RLKs were performed with Arabidopsis protoplasts transient expression system and by their ability to activate disease resistance reporter,FRK1::Luciferase(FRK1::LUC).In addition,transgenic plants overexpressing pre-screened recombinant LRR-RLKs were generated and their resistance to pathogen was verified at physiological and biochemical level.The main results of this study are as follows:(1)Among 68 recombinant LRR-RLKs,12 recombinant LRR-RLKs could significantly induce the expression of FRK1::LUC similarly to the background(EFRNT-EFRKD-EGFP).(2)Among the 12 pre-screened genes,two are root meristem growth factor receptor(RGI),RGI2 and RGI3.We replaced the extracellular domain of recombinant RGI2 and RGI3 by the extracellular domain of FLS2 and found that the expression of FRK1::LUC could still be induced.This result showed that the function of RGI2 and RGI3 kinase domains in regulating plant defense response was not dependent on the background of the fusions.(3)Recombinant RGI3 was expressed in fls2 mutant plant,We found that when treated with flg22,the transgenic plants had obvious phenotypes such as increased accumulation of reactive oxygen species and callose,enhanced inhibition on the growth of Pst DC3000 and phosphorylation of MPK3 and MPK6.These results suggest that twelve LRR-RLKs may participate in plant disease resistance,providing a theoretical reference for discovering the signaling pathway of receptor-like protein kinases.At the same time,the study of transgenic plants with recombinant RGI3 showed that the kinase domain of RGI3 could indeed participate in plant defense response.Therefore,RGI3 is likely to participate in plant root development and pathogen resistance at the same time,which will lay a foundation for further research on how this receptor kinase coordinates plant growth and resistance.