Research On The Mechanism Of Far-red Light Regulating Shoot Branching Through Hormone Signals In Tomato

In the development process of agriculture,the cultivation of horticultural crops has changed from open field cultivation to greenhouse cultivation,which can use various environmental adjustments to regulate growth of horticultural crops,thereby regulating the yield and quality.Light environment regulation is the most important environmental regulation method.Different ratios of red light/far-red light can regulate the branches of horticultural crops,thereby changing shoot architecture and affecting the final yield and quality.Tomato(Solanum lycopersicum)is one of the largest cultivation areas greenhouse vegetables in China,which has important economic value.It is also one of the important model plants in horticultural crops.Therefore,it is very important to research the influence of light environment regulation on tomato branching to obtain ideal plant architecture tomato for more yield and better quality.Auxin,cytokinins(CKs),strigolactones(SLs),and brassinosteroids(BRs)are all important hormones that regulate branching.Low ratios of red light/far red light(Low R/FR)environment will have a significant impact on the relevant endogenous hormones that regulate branching.But the specific interaction regulation mechanisms of various hormones caused by farred light treatment still uncertain in tomato.In this study,we use tomato as the experimental material and far-red light treatment as the main method to clarify the changes in the related gene expression and content of tomato auxin,cytokinin,strigolactone and brassinosteroid.The strigolactone synthetic mutants ccd7 and ccd8 are used as experimental materials and are processed by far-red light,exogenous NAA,decapitation,and exogenous 6-BA et al.to clarify the interaction between auxin,strigolactone,and cytokinin under the far-red light.In addition,we use similar approach to research the important role of brassinosteroids in the regulation of tomato branching under far-red light.The main research results are as follows:1.We confirmed the change law of tomato endogenous hormones under farred light.The wild type tomato Moneymaker was treated with far-red light and compared with the phyb1b2 mutant.It was found that the far-red light greatly inhibited the growth of tomato lateral buds,and the auxin synthesis gene FZY1 and auxin content in the apical buds were significantly increased.Strigolactone synthesis genes CCD7,CCD8,MAX1 are also significantly up-regulated,proving that the far-red light signal can significantly improve the apical dominance of tomato,and promote the biosynthesis of auxin and strigolactone.We also found that the far-red light signal significantly down-regulated the expression of cytokinin content,cytokinin synthesis gene IPTs&LOGs and the response gene RRs in the stem,indicating that the far-red light signal inhibited the synthesis and response of cytokinin in tomato.In addition,far-red light also could down-regulate brassinosteroid content and synthesis genes CPD,DWARF4,DET2,and CYP85A1 in the stem,indicating that the far-red light signal inhibits brassinosteroids.2.It was clear that the deletion of the SLs biosynthesis gene can not block the enhancement of apical dominance by far red light.When the strigolactone synthesis mutants ccd7 and ccd8 were treated with far red light,we found that the growth of lateral buds of ccd7 and ccd8 mutants were inhibited after far red light treatment,and the IAA contents and auxin synthesis gene FZY1 are all up-regulated,indicating that the signal enhancement of auxin is the initial motivation for far-red light to inhibit tomato branching.Then we use exogenous NAA to treat the ccd7 and ccd8 mutants,and we found it was consistent with the far-red light treatment.The cytokinin content and synthesis genes IPT1,IPT2 were significantly down-regulated,indicating that auxin can directly inhibit the synthesis of cytokinin.The results showed that far red light signal negatively regulates cytokinin by enhancing auxin signal to inhibit the lateral branching of tomato SLs biosynthesis mutant.The deletion of the SLs biosynthesis gene can not block the enhancement of apical dominance by far red light.3.It is confirmed that CKs is a key signal for bud outgrowth under far red light.When the tomato was treated with decapitation and exogenous sucrose under farred light,we found that both two treatments had a promoting effect on the lateral buds growth,the cytokinin content and synthesis genes IPT1,IPT2 in the stem were significantly up-regulated,indicating a decrease of cytokinin may be an important reason for the far-red light signal to inhibit tomato branching.In addition,when the strigolactone synthetic mutants ccd7 and ccd8 were treated with exogenous 6-BA under far-red light,we found that it rescued the inhibition of shoot branching.It showed that cytokinin is the key signal that inhibits the growth of lateral buds under far-red light.4.We confirmed that the inhibition of brassinosteroid is an important reason for the far-red light signal to inhibit the tomato branching.When the tomato brassinosteroid overexpression material DWF:OX was treated with far-red light,we found that far-red light could not inhibit the growth of lateral buds,indicating that brassinosteroid played an important role in the growth of tomato branching.Far red light signal may negatively regulate tomato branching by inhibiting brassinosteroid.Furthermore,when tomato was treated with decapitation and exogenous sucrose under far-red light,we found that the most of endogenous brassinosteroid content and synthesis gene were significantly up-regulated compared with far-red light treatment,which further proved that the inhibition of brassinosteroid was an important reason for the far-red light signal to inhibit the growth of tomato branching.In addition,exogenous6-BA treatment of tomato strigolactone synthetic mutants under far-red light showed that the brassinosteroid synthesis gene and content were significantly up-regulated compared with far-red light treatment,which further proved that cytokinin had positive regulation in brassinosteroid.It indicated that the inhibition of cytokinin and brassinosteroid under far-red light was an important reason for the inhibition of shoot branching.