PnTgs1-like expression during reproductive development supports a role for RNA methyltransferases in the aposporous pathway

SIENA LA; ORTIZ JPA; LEBLANC O; PESSINO SC

Bahía Blanca

Workshop; IV Ciclo de seminarios sobre avances en la caracterización genética y molecular de la apomixis en gramíneas forrajeras; 2014

CERZOS-CONICET

Apomixis (asexual reproduction via seeds) is considered to have originated from a deregulation of key steps of the sexual female development. In the past few years, comparative transcriptomic approaches in sexual and apomictic plants have produced extensive lists of apomixis candidate genes in different plant systems. Nevertheless, only a limited number of these genes have been functionally characterized, with few clues consequently available for understanding the molecular control of the trait. Recently, we have identified several cDNA fragments, high similar to genes involved in RNA biology, differentially expressed between sexual and apomictic Paspalum notatum plants. One of these candidates, N69, encodes a protein of the S-adenosyl-L-methionine-dependent methyltransferases superfamily. The objectives of this study were to extend the N69 cDNA sequence and to characterize its expression at different developmental stages during both sexual and apomictic reproduction. By using RNA-seq data we assembled a single contig representing the whole N69 CDS. The apomictic and sexual derived sequences shared 96.9% identity at the amino acid level. BLAST surveys showed significant similarity with yeast and mammalian trimethylguanosine synthase/PRIP-interacting proteins. According to these results, we renamed N69 as PNTGS1-LIKE. The function of these proteins in plants is still unknown, but yeast and mammals TGS1s are necessary for reproductive development and show dual activity as transcriptional coactivators and catalyzers of sn(o)RNA and telomerase RNA cap trimethylation. Expression of PNTGS1-LIKE during reproductive development was significantly higher in floral organs of sexual genotypes compared with apomicts in all developmental stages studied. This difference was not detected in vegetative tissues. In addition, expression levels in reproductive tissues showed a positive correlation (r2 = 0.889) with the degree of sexuality in several facultative apomictic genotypes. Besides, in situ hybridization experiments revealed that PNTGS1-LIKE expression is relatively higher in ovules of sexual plants throughout all reproductive development (from premeiosis to maturity) than in apomictic ovules. Our results suggest that down regulation of RNA methylation pathways might be critical in the transition from sexuality to apospory. Considering the broad spectrum of functions mediated by RNA methylation, further characterization of PNTGS1-LIKE function during plant reproduction will certainly help to resolve molecularly the aposporous pathway.