Abstract
TCP proteins, the plant-specific transcription factors, are involved in the regulation of multiple aspects of plant development among different species, such as leaf development, branching, and flower symmetry. However, thus far, the roles of TCPs in legume, especially in nodulation are still not clear. In this study, a genome-wide analysis of TCP genes was carried out to discover their evolution and function in Medicago truncatula. In total, 21 MtTCPs were identified and classified into class I and class II, and the class II MtTCPs were further divided into two subclasses, CIN and CYC/TB1. The expression profiles of MtTCPs are dramatically different. The universal expression of class I MtTCPs was detected in all organs. However, the MtTCPs in CIN subclass were highly expressed in leaf and most of the members in CYC/TB1 subclass were highly expressed in flower. Such organ-specific expression patterns of MtTCPs suggest their different roles in plant development. In addition, most MtTCPs were down-regulated during the nodule development, except for the putative MtmiR319 targets, MtTCP3, MtTCP4, and MtTCP10A. Overexpression of MtmiR319A significantly reduced the expression level of MtTCP3/4/10A/10B and resulted in the decreased nodule number, indicating the important roles of MtmiR319-targeted MtTCPs in nodulation. Taken together, this study systematically analyzes the MtTCP gene family at a genome-wide level and their possible functions in nodulation, which lay the basis for further explorations of MtmiR319/MtTCPs module in association with nodule development in M. truncatula.
Highlights
TCP proteins, a small family of plant-specific transcription factors, was first described in 1999 and named after its initial members TEOSINTE BRANCHED1 (TB1) in maize (Zea mays), CYCLOIDEA (CYC) in snapdragon (Antirrhinum majus), and PROLIFERATING CELL FACTORS 1 and 2 (PCF1 and PCF2) in rice (Oryza sativa) (Luo et al, 1996; Doebley et al, 1997; TCP Gene Family in MedicagoKosugi and Ohashi, 1997; Cubas et al, 1999)
TCP genes have been identified in various plant species including Arabidopsis, rice, tomato, tobacco, and strawberry as shown in Supplementary Figure S1 (Palatnik et al, 2003; Li et al, 2005; Aguilar-Martinez et al, 2007; Ori et al, 2007; Yao et al, 2007; Schommer et al, 2008; Nag et al, 2009; Giraud et al, 2010; Koyama et al, 2010b; Sarvepalli and Nath, 2011; Yang et al, 2012; Ma et al, 2014; Parapunova et al, 2014; Wang et al, 2015b; Chen et al, 2016; Lin et al, 2016; Ma et al, 2016; Wei et al, 2016; Zhou et al, 2016; Du et al, 2017; Xie et al, 2017)
The TCP family can be classified into two classes: class I and class II according to the amino acid sequences of the TCP domain (Kosugi and Ohashi, 2002; Navaud et al, 2007; Martin-Trillo and Cubas, 2010)
Summary
TCP proteins, a small family of plant-specific transcription factors, was first described in 1999 and named after its initial members TEOSINTE BRANCHED1 (TB1) in maize (Zea mays), CYCLOIDEA (CYC) in snapdragon (Antirrhinum majus), and PROLIFERATING CELL FACTORS 1 and 2 (PCF1 and PCF2) in rice (Oryza sativa) (Luo et al, 1996; Doebley et al, 1997; TCP Gene Family in MedicagoKosugi and Ohashi, 1997; Cubas et al, 1999). All TCP proteins contain a highly conserved TCP domain which is a 59-aminoacid non-canonical basic-helix-loop-helix (bHLH) motif at the N-terminus and functions in DNA binding, protein–protein interaction, and protein nuclear localization (Kosugi and Ohashi, 2002; Aggarwal et al, 2010; Martin-Trillo and Cubas, 2010; Dhaka et al, 2017). The TCP family can be classified into two classes: class I ( known as PCF class or TCP-P class) and class II ( known as TCP-C class) according to the amino acid sequences of the TCP domain (Kosugi and Ohashi, 2002; Navaud et al, 2007; Martin-Trillo and Cubas, 2010). Besides the TCP domain, all members of the CYC/TB1 TCP proteins contain an arginine-rich R domain with unknown function, which is speculated to facilitate protein– protein interaction (Cubas et al, 1999)
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