Functional analysis of Arabidopsis thaliana Class I TCP genes AtTCP7 and its roles in plant development

Plant cell division cycle is a highly complex and tightly controlled process which is regulated by both cell cycle genes conserved across kingdoms and plant-specific regulators. TCP family genes are plant-specific transcription factors reported in recent years that function in many aspects of plant growth, and broadly control the morphology of different organs via positive or negative regulating target genes expression. The initial work in our study was to identify the transcriptional factors regulating miRNA168a gene expression. A TCP family gene AtTCP7 was isolated as a putative regulator of Arabidopsis miR168a from yeast one-hybrid screening. Transgenic plants over-expressing AtTCP7 gene in Arabidopsis thaliana showed a decrease of mature miRNA168a accumulation, while later crossing analysis co-expressing 35S::AtTCP7 and pMiR168a::GUS showed a minor affection on reporter gene GUS expression, it indicated that the AtTCP7 may not directly interact with miR168a promoter in vivo. In-depth phenotypic characterization of the transgenic lines displayed a variety of growth defects and developmental delay, including shorter roots, delayed flowering and reduced fertility. Analyses at different developmental stages demonstrated that over-expression of AtTCP7 differentially affected cell size and DNA content in different organs by altering cell cycle genes expression and by restricting the interphase transition from G1 to S phase. Further expression analyses on over-expressing lines uncovered a complex network of genetic interactions between the members of the TCP family, highlighting the functional interaction especially between TCP7 and TCP23.