Genomic survey, bioinformatics analysis, and expression profiles of TCP genes in Liriodendron chinense and functional characterization of LcTCP4

TEOSINTE-BRANCHED/CYCLOIDEA/PCF (TCP) proteins are plant-specific transcription factors (TFs) that play a pivotal role in leaf development by controlling cell proliferation and differentiation. In this study, the authors systematically analyzed the phylogeny, sequence structure, domain feature and expression profiles of TCP genes in Liriodendron chinense, an ornamental tree species with peculiar leaf shape. A total of 17 LcTCP genes were identified in L. chinense genome, which could be grouped into two classes according to their features in the TCP domain. RT-qPCR analysis showed that the expression levels of four TCP genes in Class I (LcTCP21, LcTCP9, LcTCP19a, and LcTCP19b) and three genes in Class II (LcTCP4a, LcTCP4b, and LcTCP24) were consistently higher than those of the other LcTCP genes during leaf development. Degradome data analysis revealed that three LcTCP genes, LcTCP4a, LcTCP4b, and LcTCP24, are targeted by lch-miR319c. Further, LcTCP4a/b and LcTCP24 differed significantly in their expression levels between leaf buds and lobed leaves. However, the expression patterns of LcTCP21 and LcTCP9 contrasted with those of LcTCP19a and LcTCP19b, implying that leaf development in L. chinense may be regulated by a balance between the antagonistic roles of Class I and Class II LcTCP genes. Furthermore, overexpression of LcTCP4 in Arabidopsis thaliana caused a tendency of leaf margin smoothness, and down-regulated the expression levels of genes involved in cell division, AtCYCD3,1 and AtKNOLLE, indicating that LcTCP4 may influence leaf margin shape by inhibiting cell proliferation. Overall, this study provided a comprehensive assessment of the LcTCP gene family and serves as a cornerstone for subsequent functional verification of the LcTCP genes in regulating the leaf development of L. chinense.