| Tillering is one of the important characteristics of turfgrass and pasture,which directly affects the value of turfgrass and the yield of pasture.There are two main processes controlling tillers:axillary bud initiation and bud outgrowth.The axillary buds are formed in the axillary meristems at the leaf axils and regulated genetically.However,the outgrowth of the axillary bud is influenced by many factors,such as the genetic factors,plant hormone and environment.In this study,we use tall fescue(Festuca arundinacea)’Barlexas’ and ’Kentucky 31’ as experimental material to investigate the effect of gibberellic acid(GA)on the tillering.The results show that gibberellic can inhibite outgrowth of axillary bud.The study aims to elucidate that GA could repress bud outgrowth by interacting with other plant hormones and regulating the key genes specifically expressed in axillary buds in order to inhibit tiller production.FaGA2ox4,a key gene could degrade gibberellic acid,is cloned from tall fescue and overexpressed in rice(Oryza sativa)to investigate physiological functions.The results of this study are as follows:(1)Treating the tall fescue seedings with different concentration gradients(5 μM-100 μM)of GA3 solution.The tiller number of tall fescue under all concentration of GA3 is effectively inhibited.Moreover,the function of GA3 on tillering is dose-dependent.(2)Exogenous application of 25 μM GA3 to tall fescue seedlings without axillary bud showed that GA significantly inhibited the outgrowth of axillary buds instead of restraining the initiation of axillary buds.Processing tall fescue with two axillary buds at the same GA3 concentration to investigate the effect of GA,showing that GA significantly reduced the sum of axillary buds and tillers of tall fescue to inhibit tillering in turn.(3)Detecting the content of endogenous plant hormone after GA3 treatment by liquid chromatography,the result showed the content of GA in GA3-treatment was significantly higher than that of the control plants,while the content of cytokinin was down-regulated significantly due to GA3 application compared to that in the control plants.The content of IAA and SL was not significantly affected by GA3 treatment.(4)The expression of key genes involved in the pathway of GA,cytokinins,IAA and SL comparing between GA3-treated plants and control plants were detected by qRT-PCR.We found the expression of gibberellic acid synthesis gene and degradation gene were significantly up-regulated,the same as cytokinin degradation gene,while the expression of cytokinin synthetic gene was not significantly changed.There is no significant change in auxin-related genes,in contrast with strigolactone-related genes whose expression were up-regulated obviously.(5)The expression of key genes involved in the tiller bud activity was detected by qRT-PCR.The results showed that the genes playing key roles in axillary bud outgrowth were up-regulated after GA treatment,nevertheless,the genes functioned in axillary meristem initiation and tiller bud formation had no difference with control plants.(6)FaGA2ox4 was cloned from tall fescue playing important roles in the GA pathway.We constructed the pEarleyGate1305.2-FaGA2ox4 expression vector and transferred into rice,obtaining 7 positive strains detected by GUS staining.line 1,line 4 and line 8 were selected for further physiological analysis.The results showed that compared with WT,the transgenic lines produced more tillers and dwarfed,indicating that overexpression of FaGA2ox4 could effectively promote the production of tillers.In summary,GA slow down the transition from axillary buds to tiller by inhibiting the elongation of the bud,thereby inhibiting tillering.In this process,we speculate that GA may interact with other plant hormones and act through key genes involved in axillary bud activity to control the pattern of tillering,which provides a basis for the study of tiller development of cold-season turfgrass. |
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