The Mechanisms Of Auxin And Strigolactone Control Lateral Branching Outgrowth Through Cytokinin In Tomato Plants

Apical Dominance and lateral branching development play important roles in highter plant's morphological building,which not only determine the plant height,stretch and other morphological indicators,also affect the biomass,fruit yieds and other economic indicators,so the plant branching habit has become the basis of crop agronomic traits.Auxin and cytokinin,strigolactone are three plant hormones found so far to been in the regulation of lateral branching development,substantial progress about the three hormones' regulatory network have been achieved in Arabidopsis,pea,rice and other crops,but horticultural crops were scarecely reported.Tomato is a kind of vegetable crop with widely cultivated and great economic benefits,the branching habit determines that the growth of lateral branching will be an important factor to influence the biological yield,in tomato cultivation,pruning not only needs more manpower and material resources,improper operation can easily induce disease.Therefore,to clarify the internal mechanism of tomato branching development not only can effectively guide the vegetable production,improve the yield,also helpful to.enrich the regulatory mechanism of plant lateral branching development.It will lay a solid theoretical foundation for cultivating new crop varieties and rebuilding new plant morphology through biological means.In this study,we used vegetable tomato(Solanum lycopersicum L.)as the research object,by using VIGS technology,signal transduction and hormone levels to explain the mechanism of IAA,SLs and CTK in the regulation of lateral branching development in tomato.The main results are as follows:1.Studies on the relationship between auxin and strigolactone in the process of lateral branching development have shown that silencing the tomato auxin biosynthesis gene FZY and NADPH oxidase gene RBOH1 promoted bud growth,the GUS stained of the root lighter,while expression of SLs synthesis gene CCD7,CCD8,MAX1 were significantly reduced,the content of SLs(Orobanchol,isomers,Strigol,Solancol)was significantly decreased by LC/MS-MS,which suggested that changes in auxin biosynthesis and transport can affect the content of SLs.After that,we used the RBOHl-RNAi transgenic materials and dgt to verify,results showed that bud growth of RBOH1-RNAi transgenic plants and dgt was significantly longer than WT,and cytokinin synthesis gene IPT2 in the 4th stem was significantly up-regulated,negative transcriptor BRC1 in the bud and auxin transport genes PIN1 and auxin signal gene IAA3 were down regulated,which was consistent with the results that GUS stained was significantly lighter in FZY and RBOH1 gene silencing plants.Therefore,the change of auxin biosynthesis can affect the content of strigolactone by transport or signal transduction,ultimately affect the growth of lateral bud.2.Studies on the role of SLs in lateral branching development of Tomato showed that Strigolactone can inhibit branch growth by down regulating IAA3,PIN1,IPT2 gene expression,and up-regulating BRC1.Proofs of exogenous NPA and topping treatment experiments showed that NP A can inhibit IAA and promote lateral bud growth,while topping treatment reduced IAA synthesis and lateral bud growth was significantly promoted.Finally,auxin content in different parts of pTRV-M4X2 plants,pTRV plants after exogenous GR24 treatment were determined.The results showed that silencing MAX2 gene did not affect the synthesis of IAA at the apex of the plant but affect the polar transport of IAA.GR24 could inhibit the bud growth and reduce the content of IAA in roots of pTRV plants.Thus,SLs can inhibit IAA polar transport and regulate lateral branching development of tomato.3.Studies have showed silencing MAX2 gene significantly stimulated the growth of axillary buds,aftering topping,negative regulation factor BRC1 decreased significantly,IPT2 increased significantly,at the same time,the synthesis of CTK increased obviously.After exogenous NAA was applied to pTRV-MAX2 plants,the expression of IPT2 was down regulated and BRC1 was significantly up-regulated,while the CTK content was significantly decreased,That is to say,IAA and SLs can inhibit the synthesis of CTK.pTRV-FZY have increased branches and GR24 can inhibit this increase,when exogenous GR24 was applied,the expression of IPT2 was down regulated and BRC1 was significantly up-regulated in pTRV-FZY,and CTK content was significantly increased than pTRV,GR24 treatment.Then we used exogenous cytokinin biosynthesis inhibitor(CKI)to examine the role of CTK,results showed that CKI not only affected the relative gene expression of IPT2 and BRC1,may also affected the synthesis and transport of auxin.That is to say,cytokinin mediated the regulation of auxin and strigolactones in lateral branching development of tomato.