The genome-wide identification of GRF family revealing PbGRF1 regulating the leaf size in Phoebe bournei

Phoebe bournei is primarily distributed in the subtropical regions of China. As an important ornamental plant, the size of its leaves significantly impacts its ornamental value and growth. Growth-regulating factors (GRFs) play crucial roles in regulating plant development and leaf size. In this study, seven GRF genes were identified in P. bournei, among which PbGRF1 exhibited relatively high expression in leaves. We found that as leaves develop, PbGRF1 expression gradually decreases, yet larger leaves express higher levels of PbGRF1. Overexpression of PbGRF1 in Arabidopsis thaliana and Nicotiana tabacum significantly increased leaf size, and anatomical analysis revealed that the cell number in overexpression lines was markedly higher than in wild-type (WT) plants. Subcellular localization showed that PbGRF1 is localized in the nucleus, and yeast transcriptional activity assays confirmed its transcriptional activation capability. Using DNA affinity purification sequencing (DAP-seq), we screened for potential downstream target genes of PbGRF1, and based on the expression levels in transiently transformed P. bournei leaves, OLIGOCELLULA 7 (PbOLI7) was selected for further study. Subsequent yeast one-hybrid and dual-luciferase reporter assays demonstrated that PbGRF1 can bind to and activate PbOLI7, thereby regulating cell division. This study provides a theoretical basis for the regulation of leaf size in P. bournei and other forestry trees.