Genome-wide identification of the SAUR gene family and screening for SmSAURs involved in root development in Salvia miltiorrhiza

Salvia miltiorrhiza is a widely utilized medicinal plant in China. Its roots and rhizomes are the main medicinal parts and crucial in determining the quality of the herb. Previous studies reveal that auxin plays pivotal roles in S. miltiorrhiza root development. As the crucial early auxin-response genes, whether small auxin-up RNA genes (SAURs) are involved in the auxin-mediated root development in S. miltiorrhiza is worthy of investigation. In this study, 55 SmSAUR genes in S. miltiorrhiza were identified and their physical and chemical properties, gene structure, cis-acting elements, and evolutionary relationship were analyzed. The expression levels of SmSAUR genes in different organs of S. miltiorrhiza were detected by RNA-seq combined with qRT-PCR. The root development of S. miltiorrhiza seedlings was altered by the application of indole-3-acetic acid (IAA) and Pearson correlation coefficient analysis was conducted to screen SmSAURs that potentially participate in this physiological process. As the results shown, the diameter of primary lateral root was positively correlated with SmSAUR4. The secondary later root number was positively correlated with SmSAUR18 and negatively correlated with SmSAUR4. The root length showed a positive correlation with SmSAUR28 and SmSAUR37 and a negative correlation with SmSAUR38. The root fresh biomass exhibited a positive correlation with SmSAUR38 and a negative correlation with SmSAUR28. The SmSAURs mentioned above were probably involved in the auxin-mediated root development in S. miltiorrhiza. Our study presents a comprehensive overview of SmSAURs and establishes the groundwork for elucidating the molecular mechanism underlying root morphogenesis in this species.