A Preliminary Study On The Mechanism Of Gibberellin Regulation Of PpMAX4 And PpLBO1 To Promote Axillary Bud Germination In Peach Trees

The peach tree is one of the most important economic fruit trees in China and the development of the peach industry plays an important role in the improvement of our national economy.However,the budding and branching power of peach trees is strong and the branches grow vigorously,so the excessive number of branches has a great negative impact on peach production management.Therefore,reasonable regulation of peach tree branching and cultivation of appropriate varieties of peach trees with appropriate branching numbers are of great significance to improve the production efficiency of peach orchards.Gibberellins(GAs)are important hormones that regulate the growth of axillary buds.In order to elucidate the regulatory role of GA on the growth of peach axillary buds,this study investigated the effect of GA on the growth of peach axillary buds by treating peach axillary buds with exogenous GA3 and its biosynthetic inhibitor(PBZ);and the binding of DELLA(gibberellin signalling inhibitor protein)interacting protein IDD to the promoters of SL synthesis genes PpMAX4 and PpLBO1;the effect of GA on transcript levels of auxin,cytokinin and strigolactone related genes was also analysed.The main findings were as follows:1.Peach seedlings were treated with exogenous GA3 and GA biosynthesis inhibitor(PBZ).The results showed that GA3 treatment promoted the germination of axillary buds and the elongation of a few lateral buds to form lateral branches.However,PBZ treatment first inhibited the growth of peach seedlings and then exogenous GA3 significantly promoted the germination of axillary buds and the formation of more lateral.This indicates that gibberellin can promote the germination and growth of axillary buds of peach seedlings.2.Analysis of the tissue expression specificity of the strigolactone synthesis genes PpMAX4,PpLBO1-1 and PpLBO1-2 by qRT-PCR,and the results showed that the expression of PpMAX4 and PpLBO1 were both higher in the leaf axil site;In addition,the effects of exogenous GA3 treatment on the transcriptional levels of strigolactone synthesis genes PpMAX4,PpLBO1-1 and PpLBO1-2 were analysed.The results showed that exogenous GA3 treatment did not significantly regulate the transcriptional levels of PpMAX4,PpLBO1-1 and PpLBO1-2;However,when PBZ treatment was applied followed by exogenous GA3 treatment,exogenous GA3 had a significant inhibitory effect on the transcriptional levels of PpMAX4 and PpLBO1,indicating that GA could negatively regulate the transcriptional levels of PpMAX4 and PpLBO1 in the leaf axils.3.Previous studies in this trial have shown that PpIDD4,PpIDD12 and PpIDD13 can interact with DELLA proteins,which are key members of the gibberellin signalling pathway.In this study,the binding of PpIDD4,PpIDD12 and PpIDD13 to the promoters of SL synthesis genes PpMAX4,PpLBO1-1 and PpLBO1-2 was analysed using Yeast one-hybrid technology.The results showed that PpIDD12 was able to bind to the promoter regions of PpLBO1-2 and PpMAX4,,PpIDD4 and PpIDD13 did not bind significantly to PpMAX4 and PpLBO1-1.This implies that GA may be involved in the synthesis of SL by affecting the IDD-DELLA complex.4.The effects of exogenous GA3 combined with PBZ treatment on the regulation of the transcript levels of auxin transporter-related genes PpPIN3,PpPIN7,PpPIN10,PpPIN11,PpPIN13 and PpPIN15 were analysed by qRT-PCR.The results showed that the transcript levels of PpPIN3,PpPIN7 and PpPIN11 were significantly decreased after GA3 treatment compared with the control;among them,the transcript level of PpPIN7 was most significantly decreased;while the transcript levels of PpPIN10,PpPIN13 and PpPIN15 were significantly increased.This suggests that GA regulates transcription of auxin transporter-related genes during axillary bud germination in peach seedlings.5.Analysis of the transcript levels of cytokinin synthesis genes under exogenous GA3 combined with PBZ treatment was performed by qRT-PCR.The results showed that after exogenous PBZ inhibited plant growth,reapplication of GA3 could up-regulate the transcript level of PpIPT3 within 0.5 h,and the transcript level continued to be up-regulated within 24 h.In contrast,the transcript level of PpIPT9 was significantly increased after 8 h of GA3 treatment,and the up-regulation was more significant at 48 h.It showed that GA3 treatment promoted the transcription of cytokinin synthesis genes.In summary,GA was able to promote the germination of axillary buds and the formation of lateral branches in peach trees;strigolactone synthesis genes PpMAX4,PpLBO1-1 and PpLBO1-2 were all highly expressed in the leaf axils of peach branches,and their transcript levels were influenced by GA;and PpIDD12 can bind to the promoter regions of PpLBO1-2 and PpMAX4;In addition,the promotion effect of GA on peach seedling meristems correlates with the transcription of auxin and cytokinin-related genes.Based on the above experimental results,it can be shown that the promotion of germination and growth of axillary buds of peach branches by GA may be achieved to some extent by regulating the biosynthesis of SL,and may also be caused by affecting the endogenous content of auxin and cytokinin.This research topic mainly explored the role of GA in axillary bud germination of peach trees,initially elucidated the mechanism of gibberellin and PpMAX4 and PpLBO1 in regulating peach branch branching,and provided some theoretical basis for selecting and breeding excellent peach tree varieties with appropriate branch germination.