Depletion of Trimethylguanosine Synthase1 Alters Reproductive Development in Arabidopsis

SIENA L; MICHAUD C; SELLES B; PESSINO SC; INGOUFF M; ORTIZ JPA; LEBLANC O

Rosario

Workshop; 7th Series of Seminars on Advances in Apomixis Research; 2021

EU-funded Mechanisms of Apomictic Development

In flowering plants, apomixis refers to asexual reproduction through seeds. Recently, we identified a plant ortholog of yeast trimethylguanosine synthase1 (TGS1), whose expression is positively correlated with the rate of sexuality in reproductive tissues of facultative apomictic Paspalum notatum genotypes. In yeast, mammals and insects, TGS1 is encoded by a single gene and performs multiples activities. It catalyzes 50 cap trimethylation of noncoding RNAs, plays a role in the biogenesis of sn(o)RNAs, rRNA processing, and telomerase function. Moreover, it acts as a transcriptional co-activator associated with PRIP. The structure and function of TGS1 orthologs in plants remain poorly characterized. Plants containa specific copy with a WW interaction domain at the N-terminal. To explore TGS1 possible association with apomixis, we determined its expression patterns in Arabidopsis and studied its loss of function in two T-DNA insertion lines. RT-PCR revealed preferential expression of TGS1 in reproductive tissues. Transgenic plants carrying synthetic reporter constructs (pTGS1:TGS1: GUS/GFP) showed it is expressed throughout female gametogenesis and embryogenesis, but not in the nucellus. Mutant plants showed reduced fertility, and mutant allele transmission suggested gametophytic effects, with stronger bias when maternally transmitted. Cytoembryological analyses showed apomixis-like phenotypes, including multiple megaspore mother cells and embryo sacs, and extra embryos. Cell-identity markers revealed cell-fate alterations during both female gametogenesis and early seed development. Moreover, germination rate and seedling defects were observed. The knowledge gained indicates an essential role for TGS1 during sexual female gametogenesis and embryo patterning in plants.