RBCS Protein Mediates The Light Signaling That Regulates Stem Cell Function In Shoot Apical Meristem Of Arabidopsis

The development of aboveground parts of plants mainly depends on the propagation and differentiation of stem cells in shoot apical meristem(SAM).The regulatory network of growth and differentiation of SAM is very complicated.WUSCHEL(WUS),as the central participant of the regulatory network,plays a key role in maintaining the proliferation and differentiation of stem cells in SAM.Previous studies demonstrated that WUS expression is repressed during shotomorphogenesis,but can be significantly activated by light for photomorphogenesis.However,the light signaling that activates WUS expression still remains elusive.Ribulosel,5-bisphosphate carboxylase/oxygenase(RUBISCO)is a key enzyme involved in the speed-limiting step in the process of carbon fixation in plant photosynthesis.RUBISCO is consisted by eight RUBISCO large subunits(RBCL)and eight RUBISCO small subunits(RBCS).Previous studies showed that light can efficiently activate the expression of RBCS.It is unknown whether RBCS can participate in the regulation of other developmental processes besides photosynthesis.This study focuses on the possible regulation of WUS expression by RBCS.We found that RBCS may participate in the regulation of WUS expression through a longdistance trafficking from leaf to shoot apical meristem.Through a series of in vitro experiments,we found that RBCS can directly interact with WUS to form a transcription factor complex,which further binds to the promoter of WUS and activate its transcription.Since RBCS family is vital for plant,it is not possible to investigate role of RBCS in SAM activity via loss-of-funciton of RBCS.The transgenic plants with the expression of RBCSin fusion with a transcription inhibitory domain SRDX under the control of SAM specific promoter showed the phenotype of wus mutant because of the inhibiton of WUS protein.The consititutive expression of RBCS can directly activate WUS expression in SAM of plants germinated in darkness,suggesting that RBCS might mediates light signaling in activating WUS expression.Furthermore,the expression of RBCS:SRDX protein under the control of phloem specific promter also significantly inhibit the expression of WUS in SAM,demonstrating that RBCS can traffic long distance from leaf to SAM and regulates WUS expression.Taken together,our work discovered that RBCS might act as a light messenger that traffic from leaf to SAM and regulates stem cell function,resulting in the normal photomorphogenesis of plants.