Analysis of CcGASA family members in Citrus clementina (Hort. ex Tan.) by a genome-wide approach.

The Gibberellic Acid Stimulated Arabidopsis (GASA) proteins were investigated in the study to help understand their possible roles in fruit trees, particularly in Citrus. A total of 18 CcGASA proteins were identified and characterized in Citrus clementina via a genome-wide approach. It was shown that the CcGASA proteins structurally shared a conserved GASA domain but varied considerably in primary sequences and motif compositions. Thus, they could be classified into three major phylogenetic groups, G1~G3, and two groups, G1 and G3 could be further classified into subgroups. The cis- elements on all CcGASA promoters were identified and categorized, and the associated transcription factors were predicted. In addition, the possible interactions between the CcGASA proteins and other proteins were predicted. All the clues suggested that these genes should be involved in defense against biotic and abiotic stresses and in growth and development. The notion was further supported by gene expression analysis that showed these genes were more or less responsive to the treatments of plant hormones (GA3, SA, ABA and IAA), and infections of citrus canker pathogen Xanthomonas citri. It was noted that both the segmental and the tandem duplications had played a role in the expansion of the CcGASA gene family in Citrus. Our results showed that the members of the CcGASA gene family should have structurally and functionally diverged to different degrees, and hence, the representative group members should be individually investigated to dissect their specific roles.