Structural and functional annotation of the MADS-box transcription factor family in grapevine.

Background: MADS-box genes encode transcription factors that are involved in developmental control and signal transduction in eukaryotes. In plants, they are associated to numerous development processes most notably those related to reproductive development: flowering induction, specification of inflorescence and flower meristems, establishment of flower organ identity, as well as regulation of fruit, seed and embryo development. Genomic analyses of MADS-box genes in different plant species are providing new relevant information on the function and evolution of this transcriptional factor family. We have performed a true genome-wide analysis of the complete set of MADS-box genes in grapevine (Vitis vinifera), analyzed their expression pattern and establish their phylogenetic relationships (including MIKC* and type I MADS-box) with genes from 16 other plant species. This study was integrated to previous works on the family in grapevine.
Results: A total of 90 MADS-box genes were detected in the grapevine reference genome by completing current gene annotations with a genome-wide analysis based on sequence similarity. We performed a thorough in-depth curation of all gene models and combined the results with gene expression information including RNAseq data to clarifying the expression of newly identified genes and improve their functional characterization. Curated data were uploaded to the ORCAE database for grapevine in the frame of the grapevine genome curation effort. This approach resulted in the identification of 30 additional MADS box genes. Among them, ten new MIKC(C) genes were identified, including a potential new group of short proteins similar to the SVP protein subfamily. The MIKC* subgroup contains six genes in grapevine that can be grouped in the S (4 genes) and P (2 genes) clades, showing less redundancy than that observed in Arabidopsis thaliana. Expression pattern of these genes in grapevine is compatible with a role in male gametophyte development. Most of the identified new genes belong to the type I MADS-box genes and were classified as members of the Mα and Mγ subclasses. Ours analyses indicate that only few members of type I genes in grapevine have homology in other species and that species-specific clades appeared both in the Mα and Mγ subclasses. On the other hand, as deduced from the phylogenetic analysis with other plant species, genes that can be crucial for development of central cell, endosperm and embryos seems to be conserved in plants.
Conclusions: The genome analysis of MADS-box genes in grapevine, the characterization of their pattern of expression and the phylogenetic analysis with other plant species allowed the identification of new MADS-box genes not yet described in other plant species as well as basic characterization of their possible role, particularly in the case of type I and MIKC* genes.