Comprehensive analysis of SAUR gene family in citrus and its transcriptional correlation with fruitlet drop from abscission zone A.

Small auxin-up RNA (SAUR) gene family is large, and the members of which can be rapidly induced by auxin and encode highly unstable mRNAs. SAUR genes are involved in various developmental and physiological processes, such as leaf senescence, fruitlet abscission, and hypocotyl development. However, their modes of action in citrus remain unknown. Hereby, a systematic analysis of SAUR gene family in citrus was conducted through a genome-wide search. In this study, a total of 70 SAUR genes, referred to as CitSAURs, have been identified in citrus. The evolutionary relationship and the intro-exon organization were analyzed, revealing strong gene conservation and the expansion of particular functional genes during plant evolution. Expression analysis showed that the major of CitSAUR genes were expressed in at least one tissue and showed distinctive expression levels, indicating the SAUR gene family play important roles in the development and growth of citrus organs. However, there were more than 20 CitSAUR genes such as CitSARU36, CitSAUR37, and CitSAUR54 exhibiting very low expression level in all tissue tested. Twenty-three out of 70 CitSAUR genes were responded to indole-3-acetic acid (IAA) treatment, of which just CitSAUR19 was down-regulated. Additionally, 14 CitSAUR genes exhibited distinct changes during fruitlet abscission, however just 5 of them including CitSAUR06, CitSAUR08, CitSAUR44, CitSAUR61, and CitSAUR64 were associated with fruitlet abscission. The current study provides basic information for the citrus SAUR gene family and will pave the way for deciphering the precise role of SAURs in citrus development and growth as well as fruitlet abscission.