MIKCC-type MADS-box genes in Rosa chinensis: the remarkable expansion of ABCDE model genes and their roles in floral organogenesis

MIKCC-type MADS-box (MIKCC) genes encode transcription factors that have crucial roles in controlling floral organogenesis and flowering time in plants. Although this gene family has been well characterized in many plant species, its evolutionary and comprehensive functional analysis in rose is lacking. In this study, 58 non-redundant MIKCC uni-transcripts were extensively identified from rose transcriptomes. Phylogenetic analysis placed these genes into 12 clades with their Arabidopsis and strawberry counterparts, and revealed that ABCDE model (including AP1/FUL, AP3/PI, AG, and SEP clades), and SOC1 and AGL6 clade genes have remarkably expanded in Rosa chinensis, whereas genes from the FLC and AGL17 clades were undetectable. Sequence alignments suggest that the AP3/PI clade may contribute to more specific functions in rose due to a high variation of amino acid residues within its MADS-box domains. A comparative analysis of gene expression in specific floral organ differentiation stages and floral organs between R. chinensis cv. Old Blush and the closely related mutant genotype R. chinensis cv. Viridiflora (floral organs mutated into leaf-like structures) further revealed the roles of ABCDE model genes during floral organogenesis in rose. Analysis of co-expression networks provided an overview of the regulatory mechanisms of rose MIKCC genes and shed light on both the prominent roles of AP3/PI clade genes in floral organogenesis and the roles of RcAGL19, RcAGL24, and RcSOC1 in regulating floral transition in rose. Our analyses provide an overall insight of MIKCC genes in rose and their potential roles in floral organogenesis.