Genome-wide identification and expression profiling of HD-ZIP gene family in Medicago truncatula

The homeodomain-leucine zipper (HD-ZIP) transcription factors are important regulators in various developmental processes and responses to environmental stimuli. Currently, little information is available for HD-ZIP gene family in Medicago truncatula. Here we perform a genome-wide analysis of HD-ZIP gene family in M. truncatula. Totally 52 M. truncatula HD-ZIPs (MtHDZs) were identified and classified into four distinctive subfamilies (I to IV). Members clustered in the same subfamily shared similar gene structure and protein motifs. Fifty-one MtHDZs were non-evenly distributed on eight chromosomes. Segmental duplication and purifying selection mainly contributed to the expansion and retention of M. truncatula HD-ZIP gene family. Expression profiling using the publicly available microarray data revealed that MtHDZ genes exhibited distinctive tissue-specific patterns and divergent responses to drought and salt stresses. In addition, the expression profile between each paralogous pair diverged differentially. Our results identified potential targets for the genetic improvement of abiotic stress tolerance in Medicago.