Preferential retention,expression profile and potential functional diversity analysis of HD-Zip gene family in <Emphasis Type="Italic">Brassica rapa</Emphasis>

Homeodomain-Leu zipper (HD-Zip) gene family performs important biological functions related to organ development, photomorphogenesis and abiotic stress response in higher plants. However, systematic analysis of HD-Zip genes in Brassica rapa has not been performed. In the present study, a bioinformatics approach was used to identify and characterize the BraHD-Zip gene family in B. rapa. A total of 88 members were identified. All putative BraHD-Zip proteins contained a clear HD and LZ combined domain. Eighty-seven BraHD-Zips were non-randomly located on ten chromosomes. This gene family was mainly expanded following the whole genome triplication event and was preferentially over-retained relative to its neighboring genes in B. rapa. On phylogenetic analysis, the BraHD-Zips could be categorized into four distinct major groups (I–IV). Each group exhibited variant gene structures and motif distributions. Some syntenic orthologous gene pairs presented diverse expression profiles, which indicate that these gene pairs may be involved in the development of new functions during evolution. In summary, our analysis provided genome-wide insights into the expansion, preferential retention, expression profiles and functional diversity of BraHD-Zip genes following whole genome triplication in B. rapa.