The Functional Study Of SMXL4 And SMXL5 In Strigolactones Signal Transduction Pathway In Arabidopsis

Strigolactones(SLs)are a group of newly discovered plant hormone derived from ?-carotene.SLs play important roles in many process of plant development such as seeds germination,branching and secondary growth of the vascular system.In rice,SL is recognized by an ?/?-fold hydrolase DWARF14(D14),which binds to SL and DWARF53(D53),resulting in the degradation of D53 through the D3(DWARF3)-dependent proteasome pathway.Then the proteins,such as transcriptional factors repressed by D53,will be released and function.However,whether there is such a mechinism in Arabidopsis is still unfold.Though AtD14 and MAX2(Arabidopsis D3 ortholoy)had been proved to participate in SLs signaling in Arabidosis like in rice,whether suppressors like D53 exist is still to be found.There were evidences that SMXL(SUPPRESSOR OF MORE AXILLARY GROWTH2 1-LIKE)proteins might function as D53 in Arabidopsis.In this study,we examined the phenotypes of athspr(arabidopsis thaliana heat shock protein related,smxl4)in C24 ecotype and smxl4,as well as smx15 in Col ecotype to find out whether SMXL4 and SMXL5 are related to SL signaling transduction like D53 in rice.The results were as follows:1.Like other SLs deficient mutants,athspr,smx14 and smx15 were all deficient in seeds germination.2.athspr(smxl4)had more axillary branches compared to its wild-type C24.smx14 was normal in branching,however,smx14 max2-1 double mutant restored the more axillary branch phenotype of the max2-1,demonstrating that ATHSPR/SMXL4 might be a repressor of MAX2.It coinside with the result that ATHSPR/SMXL4 protein accumulated in max2 mutant.3.However,Yeast-two hybrid experiments showed that neither ATHSPR/SMXL4 nor SMXL5 interacted with MAX2 or D14 with or without GR24 treatment.Besides,SMXL4 protein did not show rapid degradation when treated with GR24 as D53 did.4.SLs affect the content and distribution of IAA through modulating the polar auxin transport(PAT).Here,PIN1 protein decreased in smx14 mutants and so as DR5.smx14 and smxl5 mutants were also more sensitive to the PAT inhibitor TIBA and NPA.5.Transcription levels of SLs marker genes in athspr mutants were similar to that in max2 mutants.SMXL3 and SMXL7 expressed less in athspr mutant but the transcription level increased remarkably after GR24 treatment,indicating that SMXL3 and SMXL7 might be important in SL signaling.