SWEET Uniporter Gene Family Expression Profile in the Pitcher Development in the Carnivorous Plant Nepenthes sp.

Transcriptome analysis of leaf and pitcher at different developmental stages in the carnivorous plant Nepenthes sp. identified 20 cDNAs of the SWEET gene family encoding sugar uniporters of classes I–IV. The structure of NSWEET proteins generally corresponded to the 3-1-3 scheme typical of SWEET proteins in eukaryotes. The variability in the expression of NSWEET genes in the mature leaf and in the three stages of pitcher development indicates the possible functional diversity of these genes. It has been suggested that class I transporters (NSWEET2d, 2f, and 2h) may participate in export of sugars from the leaf to the site of pitcher meristem initiation, while proteins NSWEET1, 2a, 2k (class I), 4a, 4b, 4d (II), and 12c (III) may participate in the delivery of sugars for the primary development of the pitcher. In subsequent stages, they can be replaced by NSWEET2b, 2c, 2e, 2i, 2j (class I), 4c (II), and 12b (III), delivering hexoses and sucrose to the growing pitcher. In the fully formed pitcher, proteins NSWEET12a (III), 2g (I), and 16 (IV) can export sugars from the digestive fluid to the leaf.