Diversity and Regulation of S-Adenosylmethionine Dependent Methyltransferases in the Anhydrobiotic Midge

Abstract

Multiple co-localized paralogs of genes in Polypedilum vanderplanki's genome have strong transcriptional response to dehydration and considered to be a part of adaptation machinery at the larvae stage. One group of such genes represented by L-isoaspartate O-methyltransferases (PIMT). In order to highlight specific role of PIMT paralogization in desiccation tolerance of the larvae we annotated and compared S-adenosylmethionine (SAM) dependent methyltransferases of four insect species. From another side we applied co-expression analysis in desiccation/rehydration time course and showed that PIMT coding genes could be separated into five clusters by expression profile. We found that among Polypedilum vanderplanki's PIMTs only PIMT1 and PIMT2 have enzymatic activity in normal physiological conditions. From in silico analysis of the protein structures we found two highly variable regions outside of the active center, but also amino acid substitutions which may affect SAM stabilization. Overall, in this study we demonstrated features of Polypedilum vanderplanki's PIMT coding paralogs related to different roles in desiccation tolerance of the larvae. Our results also suggest a role of different SAM-methyltransferases in the adaptation, including GSMT, JHAMT, and candidates from other classes, which could be considered in future studies.

Keywords: PIMT; Polypedilum vanderplanki; SAM-dependent methyltransferases; anhydrobiosis; transcriptomics.

Figure 1

Expression profiling for defined SAM-dependent methyltransferases in desiccation (yellow)-rehydration (blue) experiments on P. vanderplanki larvae: (a) self-organizing maps (SOM) clustering of P. vanderplanki MTases into three groups, namely: upregulation (blue), stable (red), and downregulation trends (turquoise); n represents the number of genes/number of MTases in the group. (b,c) A view on the expression of different MTases by type. (d) Expression of PvPimt genes in comparison to other genes from defined clusters. D00—control, D01–D48—desiccation for 1–48 h (yellow bar), R00–R48—rehydration samples for 0–48 h (blue bar).

Figure 2

Co-expression network for P. vanderplanki SAM methyltransferases. (a) General view on the network, including all Pv SAM MTases. (b) PvPimt genes co-expression heatmap. (c) PvPimt expression profiles by WGCNA cluster. D00—control, D01–D48—desiccation for 1–48 h (yellow bar), R00–R48—rehydration samples for 0–48 h (blue bar).

Figure 3

Modeling of PIMT spatial structures and docking with SAM; (a) predicted models of PIMTs using 1R18 as reference and position of SAM in different PIMTs of P. vanderplanki; (b) orientation of SAM similar to 1R18 in PIMT 1, 2, 5, 11, 12, and 14; (c) positions of SAM in PIMT 3, 6, 9, and 10; (d) different orientations of SAM in PIMT 4, 7, 8, and 13.