Function Research Of GHSBI Gene In Regulation Of Internode Length Of Cotton Fruit Branches

Cotton（Gossypium hirsutum L.）is an important economic crop,which is widely planted in the world.China is a big cotton producer,where total cotton output accounted for 23.8%of the world’s total cotton output,ranking second only to India’s 25.4%in2020.In recent years,the particularity of cotton production keeps the cost of agricultural materials at a high level,which leads to the decline of cotton farmers’enthusiasm for cotton planting,and the decrease of cotton planting area year by year.So it is imperative to develop mechanized cultivation and harvesting mode and promote popularization to improve the international competitiveness of cotton of China,with reducing the labor cost in the process of cotton production and protecting the income of cotton farmers.Mechanized harvesting has high requirements for cotton plant-type.Therefore,cotton plant-type breeding is an inevitable way to adapt to mechanized production.In the early stage,we used the standard line TM-1 of upland cotton and the natural mutant Chuannong 72318 as experimental materials,and found the candidate gene Gh SBI（Short Fruit Branch Internode）through BSA（Bulk Segregant Analysis）mapping.This project will analyze and verify the function of Gh SBI.The results are as follows.（1）Chuannong 72318 is a cotton variety with short fruit branch internode length,and its fruit branch internode length is generally less than 2cm,while the fruit node length of normal upland cotton type II is about 10cm.Scanning electron microscope（SEM）observation showed that there was significant difference in the length of xylem cells between the two materials（P<0.01）.The difference of internode length between the two materials may be caused by the difference of internode xylem cell length.（2）The q RT-PCR results showed that Gh SBI gene was mainly expressed in fruit branch stem tip and ovule,and the expression level of Gh SBI^CN was significantly higher than that of Gh SBI^TM-1.The staining results of GUS transgenic Arabidopsis showed that obvious blue could be observed in the meristem of shoot tip,bifurcation point of main stem branch,pod and flower of seedling;the staining results of GUS transgenic cotton showed that obvious blue could be observed in dormant bud of main stem branch,meristem of fruit branch,ovule and pollen.（3）GhSBI is the direct target of Ghmi R164.The results of tobacco transient expression experiment showed that the single base mutation in mi R164 target region of Ghsbi led to the decrease of the regulation efficiency of mi R164 on Ghsbi m RNA,resulting in the increase of the expression of Ghsbi.（4）Compared with the control cotton YZ-1,overexpression of Ghsbi in cotton showed shorter internode length,deeper and shrunken leaf color and sterility.The PGhsbi:Ghsbi transgenic cotton showed shorter internodes and lower seed setting rate.Transgenic experiment of cotton indicated that Gh SBI gene not only regulated the length of fruit branch,but also affected its fertility.（5）The results showed that exogenous GA₃ could promote the internode elongation of Chuannong 72318.It is speculated that Gh SBI may affect plant architecture by affecting endogenous GA₃ content.