Knockdown of a putative alanine aminotransferase gene affects amino acid content and flight capacity in the Colorado potato beetle Leptinotarsa decemlineata.

Alanine aminotransferase (ALT) plays important physiological and biochemical roles in insect. In this study, a full-length Ldalt cDNA was cloned from Leptinotarsa decemlineata. It was ubiquitously expressed in the eggs, larvae, pupae and adults. In the adults, Ldalt mRNA was widely distributed in thorax muscles, fat body, midgut, foregut, hindgut, Malpighian tubules, ventral ganglion and epidermis, with the expression levels from the highest to the lowest. Two double-stranded RNAs (dsRNAs) (dsLdalt1 and dsLdalt2) targeting Ldalt were constructed and bacterially expressed. After adults fed on dsLdalt1- and dsLdalt2-immersed foliage for 3 day, Ldalt mRNA abundance was significantly decreased by 79.5 and 71.1 %, and ALT activities were significantly reduced by 64.5 and 67.6 %, respectively. Moreover, silencing Ldalt affected free amino acid contents. Lysine was decreased by 100.0 and 100.0 %, and arginine was reduced by 87.5 and 89.4 %, respectively, in the hemolymph from dsLdalt1- and dsLdalt2-ingested beetles, compared with control ones. In contrast, proline was increased by 88.7 and 96.4 %. Furthermore, ingestion of dsLdalt1 and dsLdalt2 significantly decreased flight speed, shortened flight duration time and flight distance. In addition, knocking down Ldalt significantly increased adult mortality. These data imply that LdALT plays important roles in amino acid metabolism and in flight in L. decemlineata.