The Mechanism Of Strigolactone Inhibiting Tillering In Rice

Shoot architecture is a crucial morphological feature for plant survival and competition.It is among the key agronomic and major yield contributing factors,and over-all performance of rice(Oiyza Sativa L.).Strigolactones(SLs)are a class of carotenoid-derived hormones that have been found in root exudates of most of the plant species,the most featured role of SLs is the regulation of axillary shoot branching in many plant species,including rice.In the present study,we analyzed the SLs related genes expression in rice roots and tiller buds by simulating the soil nutrient deficiencies and drought.At the same time,external nutrition,external hormones,TIS108 and panicle removal were used to construct a series of rice population which were difference for the tiller buds growth.The endogenous plant hormone contents and the transcription of hormone signaling related genes were extensively measured to investigate how SLs works during the transformation between dormancy and gemination of rice tiller buds,and the mechanism of SLs inhibiting tillering in rice.The main results of the study are listed below.(1)SLs signaling pathway is involved in the agronomic measures for inhibiting the ineffective tillering in rice.The expression of SL biosynthesis genes and signaling genes were both up-regulated in roots and tiller buds response to nitrogen,phosphorus and water deficiency.And the stimulation of phosphorus deficiency on SLs signal transduction is stronger than nitrogen deficiency.GR24 apply can enhance the SLs signaling but inhibiting endogenous SLs biosynthesis in rice.Bisedes,obvious position effect and time-dependent effect of GR24 apply on inhibiting tiller outgrowth were observerd during our research.(2)SLs were found to be inhibiting rice tiller outgrowth with reducing CK contents in tiller buds.Furthermore,both exogenous SLs and endogenous SL-synthesis inhibitor supply could also affect the expression level of OsCKX genes but not of the OsIPT genes.Comparison of OsCKX genes expression pattern under exogenous SL and CK supply suggested that SLs induced OsCKXs expression was most likely via CK-induced independent pathway.These results combined with cytokinin type-A RR genes expression in bud suggested that SLs could act directly in buds to control CK signalling,subsequently affecting their outgrowth.SLs functioned antagonistically with CK in regulating the outgrowth of tiller buds,by promoting the OsCKX genes expression in buds.(3)RNA-Seq provide high throughput measurement of transcriptome change in the bud inhibition of strigolactone in rice.Comparison of transcript expression levels among three treatments viz.(1)intact(Co)vs removed panicle(RP)and(2)RP vs RP combined with GR24(GR)revealed the involvement of numerous genes associated with hormone signal transduction.GR24 supply could reduce the RP-induced enhancement of auxin early response genes,independent of ARF.CK signals were also expressively induced by RP,but type-A ARR were the only genes responding to GR without any other CK associated genes.Additionally,auxin transport and CK degradation were also noticed to be modified through flavonoid,phenylpropanoid and benzoxazinoid biosynthesis by RP and GR.Contemplating the results obtained so far,it is possible to open up new horizons of research to reveal the interactions among SLs,auxin and CK in controlling the shoot branching of rice.