Genome-Wide Investigation and Characterization of SWEET Gene Family with Focus on Their Evolution and Expression during Hormone and Abiotic Stress Response in Maize.

The sugar will eventually be exported transporters (SWEET) family is an important group of transport carriers for carbon partitioning in plants and has important functions in growth, development, and abiotic stress tolerance. Although the SWEET family is an important sugar transporter, little is known of the functions of the SWEET family in maize (<i>Zea mays</i>), especially in response to abiotic stresses. To further explore the response pattern of maize SWEET to abiotic stress, a bioinformatics-based approach was used to predict and identify the maize <i>SWEET</i> gene (<i>ZmSWEET</i>) family. Twenty-four <i>ZmSWEET</i> genes were identified using the MaizeGDB database. Phylogenetic analysis resolved these twenty-four genes into four clades. One tandem and five segmental duplication events were identified, which played a major role in <i>ZmSWEET</i> family expansion. Synteny analysis provided insight into the evolutionary characteristics of the <i>ZmSWEET</i> genes with those of three graminaceous crop species. A heatmap showed that most <i>ZmSWEET</i> genes responded to at least one type of abiotic stress. By an abscisic acid signaling pathway, among which five genes were significantly induced under NaCl treatment, eight were obviously up-regulated under PEG treatment and five were up-regulated under Cd stress, revealing their potential functions in response to abiotic stress. These findings will help to explain the evolutionary links of the <i>ZmSWEET</i> family and contribute to future studies on the functional characteristics of <i>ZmSWEET</i> genes, and then improve abiotic stress tolerance in maize through molecular breeding.