Research advances in the plant TCP transcription factors

Abstract

<p indent="0mm">Transcription factors (TFs) are a group of protein molecules that can bind to a specific gene with a specific sequence specificity, thus ensuring that the target gene is expressed at a specific time and in space at a specific intensity. The plant-specific TFs of the TCP family (for Teosinte branched 1 in corn, CYCLOIDEA (CYC) in snapdragon (<italic>Antirrhinum majus</italic>) and PROLIFERATING CELL FACTOR 1/2 in rice) are characterized by an N-terminal non-canonical beta helix-loop-helix (bHLH) domain known as the TCP domain, and regulate the spatiotemporal expression of genes by binding to specific promoter sequences. TCP TFs play important roles in regulating the development of roots, stems, leaves, flowers, fruits, and vascular tissues, and participate in physiological processes such as plant secondary metabolism, plant immunity, and the responses to biotic and abiotic stress. The TCP TF family is conserved and widespread in plants. Based on the TCP domain sequence, TCP TFs are categorized into Class I and Class II; based on the amino acid sequence of the basic region and bHLH domain, the Class II TCP TFs can be further divided into CINCINNATA (CIN)-like TCPs (CIN) and CYC-like TCPs (CYC-C). In recent years, increasing numbers of studies have shed light on how TCP TFs regulate plant growth and development, especially on the functions of upstream regulators and downstream target genes. Plants have evolved multiple ways to accurately regulate their downstream related factors, and their own gene expression is also strictly regulated. TCP genes have also been analyzed in various plants and found to take part in the regulation of circadian rhythms and the biosynthesis and signaling pathways of plant hormones, among other functions. Other studies have investigated the regulatory relationships between TCP TFs and microRNAs. Additionally, members of the TCP family are often functionally redundant, making it difficult to study their functions; therefore, gene-editing technology and high-throughput sequencing have opened up new avenues to study this TF family. Here, we summarize recent advances in our understanding of how TCP activity is translated to the dynamic spatiotemporal control of cell-fate determination, life-cycle transitions, dormancy release, seed germination, leaf development, outgrowth of shoot branches, growth-repressing microRNAs, and interactions with the chromatin remodeling machinery to modulate phytohormone responses. Furthermore, we discuss existing problems and future directions in TCP research, in particular the role of TCP-related protein modification in plant growth and development and stress responses. Finally, we provide perspectives on the future research that is needed to gain a deep understanding of the diverse regulatory networks of TCP TFs in plant growth and development.