Molecular cloning and characterization of a putative proline dehydrogenase gene in the Colorado potato beetle,Leptinotarsa decemlineata

Leptinotarsa decemlineata adults exhibit a season-dependent activity. In spring, post-diapause beetles often fly a long distance from overwintering sites to potato fields. In summer and autumn, the flight ability is sharply reduced. Proline is the main energy substrate ofL. decemlineata during flight and proline dehydrogenase （ProDH） catalyzes the first step in proline catabolism. Here we identified a putative LdProDHgene; it had three cDNA isoforms which shared the same 5＇UTR and coding region, but differed in the lengths of 3＇UTRs （515, 1 092 and 1 242 bp for isoforms-1, -2 and -3, respectively）. LdProDH encoded a 616 amino acid protein that showed high sequence similarity to ProDH-like proteins from other insect species. LdProDHwas expressed in the third and fourth instars larvae and adults, but not in pupae. Dietary ingestion of bacterially expressed LdProDH- dsRNA by adults significantly decreased its messenger RNA （mRNA） level, and caused an elevation of free proline content in the hemolymph. Further observation revealed that three canonical polyadenylation signals （AATAAA） were tandemly located in the 3＇UTR of isoform-3. The first, second and third polyadenylation sites gave rise to isoforms-1, -2 and -3, respectively. Analysis of the genomic DNA uncovered that the three isoforms resulted from alternative polyadenylation. The mRNA level of isoform-1, which expressed at low levels in pre-diapause adults, became abundant in post-diapause beetles. It is indicated that the LdProDH expression is fine-tuned through 3＇UTR to control proline catabolism for the season-dependent activity ofL. decemlineata adults.