Genome-wide identification and characterization of MADS-box family genes related to organ development and stress resistance in Brassica rapa.

BACKGROUND: MADS-box transcription factors (TFs) are important in floral organ specification as well as several other aspects of plant growth and development. Studies on stress resistance-related functions of MADS-box genes are very limited and no such functional studies in Brassica rapa have been reported. To gain insight into this gene family and to elucidate their roles in organ development and stress resistance, we performed genome-wide identification, characterization and expression analysis of MADS-box genes in B. rapa.

RESULTS: Whole-genome survey of B. rapa revealed 167 MADS-box genes, which were categorized into type I (Mα, Mβ and Mγ) and type II (MIKC(c) and MIKC*) based on phylogeny, protein motif structure and exon-intron organization. Expression analysis of 89 MIKC(c) and 11 MIKC* genes was then carried out. In addition to those with floral and vegetative tissue expression, we identified MADS-box genes with constitutive expression patterns at different stages of flower development. More importantly, from a low temperature-treated whole-genome microarray data set, 19 BrMADS genes were found to show variable transcript abundance in two contrasting inbred lines of B. rapa. Among these, 13 BrMADS genes were further validated and their differential expression was monitored in response to cold stress in the same two lines via qPCR expression analysis. Additionally, the set of 19 BrMADS genes was analyzed under drought and salt stress, and 8 and 6 genes were found to be induced by drought and salt, respectively.

CONCLUSION: The extensive annotation and transcriptome profiling reported in this study will be useful for understanding the involvement of MADS-box genes in stress resistance in addition to their growth and developmental functions, which ultimately provides the basis for functional characterization and exploitation of the candidate genes for genetic engineering of B. rapa.