Molecular and adaptive evolution of Nep2 gene from carnivorous plant Nepenthes

Abstract

Nepenthes get their nutrient by carnivory using their pitchers. A prey drowned in the pitcher fluid, will be digested by enzymes called nepenthesin, i.e. nepenthesin II. The structure of nepenthesin II-encoding gene might be related to the role of the enzyme. Therefore, the objective of this study was to examine the molecular and adaptive evolutions of Nep2 gene expressing nepenthesin II. We analyzed 29 Nepenthes species that represent most habitat types. Total DNA was extracted from silica-dried leaf samples and amplification of Nep2 gene was performed using degenerate primers. Homology searching was conducted using BLASTn, followed by computation of isoelectric point of the enzyme, and testing for positive selection using Mega 5. The result showed 29 DNA sequences of Nep2 gene have no introns. Intron-less Nep2 gene will produce nepenthesin II rapidly to digest the prey. The gene experienced significant positive selection on N. sumatrana, a species inhabits the lowest altitude habitats amongst Sumatran species. An obvious adaptive phenotype is the development of two unusual types of lower pitchers to obtain nutrient in lowland habitats. In conclusion, molecular and adaptive evolutions of Nep2 gene characterized Nepenthes as highly adaptable plants that actively respond to the environmental stress.