Genome-wide identification of GROWTH-REGULATING FACTORs in Liriodendron chinense and functional characterization of LcGRF2 in leaf size regulation

GROWTH-REGULATING FACTORs (GRFs) play a pivotal role in the regulation of leaf size in plants and have been widely reported in plants. However, their specific functions in leaf size regulation in Liriodendron chinense remains unclear. Therefore, in this study, we identified GRF genes on a genome-wide scale in L. chinense to characterize the roles of LcGRFs in regulating leaf size. A total of nine LcGRF genes were identified, and these genes exhibited weak expression in mature leaves but strong expression in shoot apex. Notably, LcGRF2 exhibited the highest expression level in the shoot apex of L. chinense. Further RT-qPCR assay revealed that the expression level of LcGRF2 gradually decreased along with the leaf development process, and also displayed a gradient along the leaf proximo-distal and medio-lateral axes. Furthermore, overexpression of LcGRF2 in Arabidopsis thaliana resulted in increased leaf size, and significantly up-regulated the expression of genes involved in cell division like AtCYCD3;1, AtKNOLLE, and AtCYCB1;1, indicating that LcGRF2 may influence leaf size by promoting cell proliferation. This work contributes to a better understanding of the roles and molecular mechanisms of LcGRFs in the regulation of leaf size in L. chinense.