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

Abstract

BackgroundIn flowering plants, apomixis (asexual reproduction via seeds) is widely believed to result from failure of key regulators of the sexual female reproductive pathway. In the past few years, both differential display and RNA-seq comparative approaches involving reproductive organs of sexual plants and their apomictic counterparts have yielded extensive lists of candidate genes. Nevertheless, only a limited number of these genes have been functionally characterized, with few clues consequently available for understanding the molecular control of apomixis. We have previously identified several cDNA fragments with high similarity to genes involved in RNA biology and with differential amplification between sexual and apomictic Paspalum notatum plants. Here, we report the characterization of one of these candidates, namely, N69 encoding a protein of the S-adenosyl-L-methionine-dependent methyltransferases superfamily. The purpose of this work was to extend the N69 cDNA sequence and to characterize its expression at different developmental stages in both sexual and apomictic individuals.ResultsMolecular characterization of the N69 cDNA revealed homology with genes encoding proteins similar to yeast and mammalian trimethylguanosine synthase/PRIP-interacting proteins. These proteins play a dual role as ERK2-controlled transcriptional coactivators and mediators of sn(o)RNA and telomerase RNA cap trimethylation, and participate in mammals and yeast development. The N69-extended sequence was consequently renamed PnTgs1-like. Expression of PnTgs1-like during reproductive development was significantly higher in floral organs of sexual genotypes compared with apomicts. This difference was not detected in vegetative tissues. In addition, expression levels in reproductive tissues of several genotypes were negatively correlated with facultative apomixis rates. Moreover, in situ hybridization observations revealed that PnTgs1-like expression is relatively higher in ovules of sexual plants throughout development, from premeiosis to maturity. Tissues where differential expression is detected include nucellar cells, the site of aposporous initials differentiation in apomictic genotypes.ConclusionsOur results indicate that PnTgs1-like (formerly N69) encodes a trimethylguanosine synthase-like protein whose function in mammals and yeast is critical for development, including reproduction. Our findings also suggest a pivotal role for this candidate gene in nucellar cell fate, as its diminished expression is correlated with initiation of the apomictic pathway in plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0297-0) contains supplementary material, which is available to authorized users.

A reference floral transcriptome of sexual and apomictic Paspalum notatum

“…RACE amplification experiments were in fact conducted successfully for several candidates [55–57], but the recovery of full genic sequences turned out very difficult and time consuming, especially for complex or long transcripts. Moreover, the characterization of all allelic/splice variants expressed in flowers was virtually impracticable.…”

“…Some of the candidates identified from Paspalum are currently under examination in order to investigate their positional and functional linkage with apomixis, e.g. LORELEI -like PNGAP1 [55], PNSERK [56] and PNTGS1 -like [57]. …”

Physiological and proteomic responses to salt stress in chloroplasts of diploid and tetraploid black locust (Robinia pseudoacacia L.)

“…When plants are exposed to salt stress, electron transport may be inhibited and photoinhibition occurs as a consequence. ATP synthase produces ATP from ADP via a proton gradient across a membrane, and ATP synthase subunits (alpha, beta and delta) are involved in the photosystem electron transfer reaction 30 . Chlorophyll a/b-binding (CAB) proteins, important components of the major light-harvesting complex, are the apoproteins of photosystem II (PSII) 31 .…”

Trimethylguanosine Synthase1 (TGS1) Is Essential for Chilling Tolerance

“…TMG cap formation depends on TGS proteins and plays a key role in biogenesis of both small nuclear RNA (snRNA) and a subset of small nucleolar RNA (snoRNA), molecules that have important roles in a wide range of cellular functions (Burroughs et al, 2014). Although plant homologs to yeast and animal TGS1 proteins have been noted (Mouaikel et al, 2002) and expression analysis of one homolog conducted (Siena et al, 2014), there has previously been no characterization of TGS1 in plants.…”