Genome-wide identification and expression analyses of SWEET gene family reveal potential roles in plant development, fruit ripening and abiotic stress responses in cranberry (<i>Vaccinium macrocarpon</i> Ait)

The sugars will eventually be exported transporter (SWEET) family is a novel class of sugar transporters that play a crucial role in plant growth, development, and responses to stress. Cranberry (<i>Vaccinium macrocarpon</i> Ait.) is a nutritious berry with economic importance, but little is known about <i>SWEET</i> gene family functions in this small fruit. In this research, 13 <i>VmSWEET</i> genes belonging to four clades were identified in the cranberry genome for the first time. In the conserved domains, we observed seven phosphorylation sites and four amino acid residues that might be crucial for the binding function. The majority of <i>VmSWEET</i> genes in each clade shared similar gene structures and conserved motifs, showing that the <i>VmSWEET</i> genes were highly conserved during evolution. Chromosomal localization and duplication analyses showed that <i>VmSWEET</i> genes were unevenly distributed in eight chromosomes and two pairs of them displayed synteny. A total of 79 <i>cis</i>-acting elements were predicted in the promoter regions of <i>VmSWEETs</i> including elements responsive to plant hormones, light, growth and development and stress responses. qRT-PCR analysis showed that <i>VmSWEET10.1</i> was highly expressed in flowers, <i>VmSWEET16</i> was highly expressed in upright and runner stems, and <i>VmSWEET3</i> was highly expressed in the leaves of both types of stems. In fruit, the expression of <i>VmSWEET14</i> and <i>VmSWEET16</i> was highest of all members during the young fruit stage and were downregulated as fruit matured. The expression of <i>VmSWEET4</i> was higher during later developmental stages than earlier developmental stages. Furthermore, qRT-PCR results revealed a significant up-regulation of <i>VmSWEET10.2</i>, under osmotic, saline, salt-alkali, and aluminum stress conditions, suggesting it has a crucial role in mediating plant responses to various environmental stresses. Overall, these results provide new insights into the characteristics and evolution of <i>VmSWEET</i> genes. Moreover, the candidate <i>VmSWEET</i> genes involved in the growth, development and abiotic stress responses can be used for molecular breeding to improve cranberry fruit quality and abiotic stress resistance.