IICAR   25568
INSTITUTO DE INVESTIGACIONES EN CIENCIAS AGRARIAS DE ROSARIO
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Trimethylguanosine synthase depletion alters reproductive development in Arabidopsis thaliana
Autor/es:
SIENA LA; ORTIZ JPA; INGOUFF M; PESSINO SC; MICHAUD C; LEBLANC O
Lugar:
Zavalla
Reunión:
Workshop; Seminario Apomixis; 2019
Institución organizadora:
Grupo Apomixis-IICAR
Resumen:
In flowering plants, apomixis refers to asexual reproduction through seeds. In previous work, we reported differential expression for genes encoding RNA methyltransferases between sexual and apomictic plants in the tropical grass Paspalum notatum. In particular, the expression of a plant-specific copy of trimethylguanosine synthase 1 (TGS1) was positively correlated with the rate of sexuality in facultative apomicts and in situ hybridization revealed differential spatio-temporal expression patterns associated with the reproductive mode. In yeast, mammals and insects, TGS1 is encoded by a single gene and performs a dual activity. First, it catalyzes cap trimethylation of noncoding RNAs and plays a role in the biogenesis of sn(o)RNAs that are essential for splicing, rRNA processing and telomerase function. Second, it acts as a transcriptional co-activator associated with PRIP. TGS1 orthologs structure and function remain poorly characterized in plants, which contain at least a second copy of the gene with an N-terminal extension carrying a WW interaction domain. To study the function of TGS1 and explore its possible association with apomixis in the Arabidopsis thaliana plant model, we characterized plants defective for two genes: TGS1 (AT1G30550, similar to the canonical TGS1 present in all eukaryotes) and TGS1‐like (AT1G45231, plant-specific copy including an N-terminal extension), by using genetic, cellular biology and transcriptomic approaches. RT-PCR revealed preferential expression of TGS1-like in reproductive tissues. Transgenic plants carrying synthetic reporter constructs (pTGS1-like:TGS1-like:GUS/GFP) showed expression in sub-terminal root tips, lateral root meristems, stomatas, ovule primordia, developping male and female gametophytes, egg cells and embryos. Homozygous plants for TGS1-like mutant alleles showed reduced fertility (~60% of aborted seeds) and reciprocal crosses between wild type plants and heterozygous and homozygous plants suggested gametophytic effects with stronger bias when the mutant allele was transmitted through maternal gametes. In agreement, paternal alleles of TGS1-like reactivated early during zygote development (1 DAP) and were expressed at least up to 10 DAP, indicating that a wild type paternal allele cannot rescue maternal copy depletion during early embryo develoment. Cytoembryological analyses of tgs1-like and the double mutant tgs1-like/tgs1 revealed apomixis-reminiscent defects during megagametogenesis and embryo development, including multiple megaspore mother cells, multiple embryo sacs and supernumerary embryos. Cell-identity markers revealed cell fate alterations during both female gametogenesis and early seed development. In particular, abnormal patterns where detected when monitoring the expression of auxin response reporter genes transmitted paternally in early tgs1-like/+ embryos. The knowledge gained from this work indicates an essential role for TGS1-like in cell fate specification during sexual female gametogenesis as well as in embryo patterning.