Genome-wide analysis of the citrus B3 superfamily and their association with somatic embryogenesis
Abstract Background In citrus, genetic improvement via biotechnology is hindered by the obstacle of in vitro regeneration via somatic embryogenesis (SE). Although a few of B3 transcription factors are reported to regulate embryogenesis, little is known about the possible roles of B3 superfamily during SE especially in citrus. Results In this study, a total of 72 (CsB3) and 69 (CgB3) putative B3 superfamily members were identified in the sweet orange (Citrus sinensis) and pummelo (C. grandis) genomes, respectively, each comprised four gene families and 14 phylogenetic classes. The B3 genes were unevenly distributed over citrus chromosomes and other non-anchored scaffolds. Genome duplication analysis indicated that the segmental and tandem duplication events have significantly contributed to the expansion of the citrus B3 superfamily. The evolutionary relationships among the B3 family members and their putative functions were deduced based on the results of phylogenetic analysis. Furthermore, transcriptomic analysis showed that citrus B3 genes have differential expression levels in various tissues, suggesting distinct biological roles of different members. Expression analysis revealed that the B3 superfamily members showed four types of expression profiles during SE in citrus and may play functional roles during SE, especially at late SE stages. Of them, CsARF19 is specifically expressed in sweet orange and at markedly higher levels in the embryogenic callus (EC), implying its possible involvement in EC initiation. Conclusions This study provides a genome-wide analysis of citrus B3 superfamily, including its genome organization, evolutionary features and expression profiles, which contributes to a better understanding of the B3 genes in citrus and their association with SE.