**Xing Ding, Jinhua Li, Yu Pan, Yue Zhang, Lei Ni, Yaling Wang and Xingguo Zhang \***

Key Laboratory of Horticulture Science for Southern Mountainous Regions (Chinese Ministry of Education), College of Horticulture and Landscape Architecture, Southwest University, Chongqing 400715, China; dingdingxing@email.swu.edu.cn (X.D.); ljh502@swu.edu.cn (J.L.); pany1020@swu.edu.cn (Y.P.); zy18109037077@163.com (Y.Z.); m15090062251@163.com (L.N.); yalingwangx@163.com (Y.W.)

**\*** Correspondence: zhangdupian@swu.edu.cn; Tel.: +86-23-68250974

Received: 12 April 2018; Accepted: 23 May 2018; Published: 27 May 2018

**Abstract:** The UGlcAE has the capability of interconverting UDP-D-galacturonic acid and UDP-D-glucuronic acid, and UDP-D-galacturonic acid is an activated precursor for the synthesis of pectins in plants. In this study, we identified nine *UGlcAE* protein-encoding genes in tomato. The nine *UGlcAE* genes that were distributed on eight chromosomes in tomato, and the corresponding proteins contained one or two trans-membrane domains. The phylogenetic analysis showed that *SlUGlcAE* genes could be divided into seven groups, designated *UGlcAE1* to *UGlcAE6*, of which the *UGlcAE2* were classified into two groups. Expression profile analysis revealed that the *SlUGlcAE* genes display diverse expression patterns in various tomato tissues. Selective pressure analysis indicated that all of the amino acid sites of SlUGlcAE proteins are undergoing purifying selection. Fifteen stress-, hormone-, and development-related elements were identified in the upstream regions (0.5 kb) of these *SlUGlcAE* genes. Furthermore, we investigated the expression patterns of *SlUGlcAE* genes in response to three hormones (indole-3-acetic acid (IAA), gibberellin (GA), and salicylic acid (SA)). We detected firmness, pectin contents, and expression levels of UGlcAE family genes during the development of tomato fruit. Here, we systematically summarize the general characteristics of the *SlUGlcAE* genes in tomato, which could provide a basis for further function studies of tomato *UGlcAE* genes.

**Keywords:** *Solanum lycopersicum*; *UGlcAE* gene family; identification; characterization; plant hormones; gene expression
