An Auxin Responsive CLE Gene Regulates Shoot Apical Meristem Development In Arabidopsis

Auxin is synthesized actively in growing tissues and organs in plant such as apical and shoot tips,and transported,in a polar maner,to various parts of the plant to regulats plant growth and development.Auxin,regulates most,if not all,aspects of plant growth and development,including lateral root formation,organ patterning,apical dominance and tropisms.Auxin regulates plant growth and development in a dose-dependment manner,low concentrations of auxin promots plant growth,whereas high-concentration of auxin inhibits plant growth.The young cells are sensitive to auxin,but the senescent cells are not.Peptide hormones are peptides with hormone activities.Peptide hormones regulate many cellular processes in animals,bacteria and yeast.Plant peptide hormones play an important role in regulating several aspects of plant growth and development,including plant apical meristem-development,pores formation,and flower organ development.So far,nearly 20 different types of plant peptide hormones have been identified.Both auxin and peptide hormones can regulate plant growth and development,and there is cross-talk between auxin and some of the peptide hormones.For example,CLEL(CLE-like)peptides is known to regulate auxin transport,and the expression of PLS and RGF genes are regulated by auxin.However,the relationship between the auxin and CLE(CLAVATA3/ENDOSPERM SURROUNDING REGION)peptides remains largely unkown.Here we report the identification of OsCLE48,a rice(Oryza sativa)CLE gene,as an auxin response gene,and the functional characterization of OsCLE48 in Arabidopsis.Phylogenetic analysis showed that OsCLE48 is most closely related to a subgroup of Arabidopsis A-type CLE proteins,CLE1–CLE7.RT-PCR results showed that the expression of OsCLE48 in rice seedings was elevated after treated by exogenously IAA(indole-3-acetic acid).Expression of integrated OsCLE48p-GUS reporter gene in transgenic Arabidopsis plants was also induced by exogenously IAA treatment.These results indicate that OsCLE48 is an auxin responsive gene.Histochemical staining showed that GUS activity was detected in all the tissue and organs of the OsCLE48p-GUS transgenic Arabidopsis plants.qRT-PCR results showed that OsCLE48 is expressed in all tissues and organs examined in rice including stems,roots,shoots,leaves and spikelets.Expression of OsCLE48 under the control of the 35 S promoter in Arabidopsis inhibited shoot apical meristem development.Expression of OsCLE48 under the control of the CLV3 native regulatory elements almost completely complemented clv3-2 mutant phenotypes.RT-PCR results showed that the expression of gene WUS was also restored to the wild-type levels in the transgenic plants.These results suggest that OsCLE48 is functionally similar to CLV3.On the other hand,expression of OsCLE48 under the control of the 35 S promoter in Arabidopsis has little effects on root apical meristem development,and transgenic rice plants overexpressing OsCLE48 are morphologically indistinguishable from wild type plants.These results suggest that the functions of some CLE peptides may not be fully conserved in Arabidopsis and rice.Taken together,our results showed that OsCLE48 is an auxin responsive peptide hormone gene,and it regulates shoot apical meristem development when expressed in Arabidopsis.