Abstract: SAUR（Small auxin up-regulated RNA） is a plant-specific early auxin response gene. In order to study the function of CclSAUR49 in regulating limonoid metabolism in citrus，six CclSAUR49 overexpression plants（OE1–OE6）and two RNA interference plants（Ri1 and Ri2）were generated through genetic transformation with epicotyl of Poncirus trifoliata Raf. The growth performance of transgenic and wild type plants was observed and compared. The epidermal microstructure and tissue structure of leaves were observed by electron microscopy and semi-thin sections，respectively. The contents of auxin and limonoids in the leaves were also detected. The morphological performance of the six overexpression plants was different. Compared with the wild type，the shoot length of OE2 increased by 23.21%，the number of internodes increased，and the leaf length increased by 17.97%. The branch growth of two RNA interference expression plants（Ri1 and Ri2）was less than 23.95% and 46.82%. The main leaf vein diameter of 2/3 overexpression plants increased，while Ri2 decreased. The expressions level of CclSAUR49 in the leaves of six overexpression plants were significantly up-regulated，which was 2.47–73.29 times of the wild type. The expression of CclSAUR49 in the leaves of two RNA interference expression plants were significantly inhibited，and the expression levels were 22.66% and 47.22% of the wild type. The expression level of CclSAUR49 in the leaves of transgenic plants was significantly positively correlated with its auxin content，and was significantly positively correlated with the expression levels of auxin biosynthesis（YUC6 and YUC10），transport（PIN3）and signal transduction（CiARF7 and CiARF9）genes in the transgenic plants. The content of limonoids in the leaves of four overexpression plants decreased，and the content of limonoids in the leaves of one RNA interference expression plant（Ri1）increased significantly. In the RNA interference expression plants，the content of limonoids was significantly negatively correlated with the content of auxin. The above results indicate that CclSAUR49 can promote the growth and development of citrus plants，and regulate the auxin level in plant tissues by affecting the expression of genes in auxin biosynthesis，transport and signal transduction pathways，thereby affecting the metabolism of limonoids.

Key words: citrus, CclSAUR49, genetic transformation, auxin, limonoids