Molecular characterization and functional analysis of two trehalose transporter genes in the cabbage beetle, Colaphellus bowringi

The trehalose, major blood sugar in insects, enhances stress resistance of diapausing individuals in adverse environment and provides an energy source for reproduction. Trehalose transporters (TRETs) play an important role in transport of trehalose from trehalose-producing tissues, e.g. fat body, to trehalose-consuming tissues. Although studies have shown that trehalose contributes to diapause and reproduction, the function of TRETs in these processes remains unclear. In this work, we cloned two TRET genes, TRET1a and TRET1b, from the cabbage beetle Colaphellus bowringi, which is capable of entering reproductive diapause under long-day conditions. We also analyzed the expression profiles of these two genes and investigated their potential roles in diapause and reproduction. The results suggested that both TRET1a and TRET1b belong to sugar-transporter and major facilitator superfamilies. Interestingly, TRET1a was highly expressed in the fat bodies of diapause-destined (DD) females but TRET1b was predominantly expressed in the ovaries of non-diapause-destined (NDD) females. Hormonal induction indicated that juvenile hormone induced TRET1b but repressed TRET1a at transcriptional levels. Methoprene-tolerant and Krüppel homolog 1 mediated the JH-suppressed TRET1a expression but were not involved in the regulation of TRET1b expression by JH. RNAi of TRET1a in DD females elevated the trehalose content in the fat bodies and suppressed the expression of a couple of genes related to stress resistance, which is a critical diapause trait. Knockdown of TRET1b in NDD females reduced the trehalose content in the ovaries but had no apparent effect on the ovary development and yolk deposition. These data suggest that TRET1a and TRET1b could regulate the trehalose content in specific tissues and may play potential roles in reproductive diapause in the females of C. bowringi.