Biological Role Of OsRAC3 In Rice

Rac/ROPs are plant-unique small G proteins,which are involved in multiple signaling pathways as molecular switches.Such as,the polar growth of pollen tube and root hair,ROS production,hormone responses and formation of secondary cell wall.Rac/ROPs widely exist in plants,there are 11 members in Arabidopsis,6 members in barley and 7 members in rice.However,the functional studies of Rac/ROP family genes have been poorly reported in rice development.In this work,we observed the spatio-temporal expression pattern of OsRAC3.We analyzed related phenotypes of CA-osrac3 transgenic plants and explored its preliminary mechanism.The results are presented as follows:1.The expression vector of OsRAC3pro:GUS has been constructed and introduced into rice and the transgenic plants were obtained.At different stages of rice,GUS staining assays show that OsRAC3 is strongly expressed in adventitious root of seeding,tip of adventitious root and node where adventitious roots initiate;OsRAC3 is also expressed in young leaves,leaf sheathes and leaf pillows.It is also expressed in stamens,pistils,lemma and palea of spikelet.2.At vegetative growth stage of CA-osrac3 plants,we found that the number of crown roots increased compared with wild type.In order to explore its mechanism,the hormone treatment experiment was conducted with 6-BA and NAA.The results showed,the sensitivity of CA-osrac3 mutant to cytokinin was reduced.It suggests that OsRAC3 may regulate the development of crown root though cytokinin pathway.3.We also observed that over-expression of CA-osrac3 increased grain size and weight.Scanning electron microscope analysis of CA-osrac3 spikelets before heading shows that the epidermal cells of spikelet hulls are longer than wild type.Taken together,OsRAC3 is expressed specifically in roots and several tissues on aerial part of rice,it may play a role in regulating grain size and development of crown roots in cytokinin-dependent pathway.