Expression profiles of methyltransferases and RdDM proteins in Eragrostis curvula plants with sexual and apomictic reproduction

SELVA JP; PESSINO S; ROMERO J; LEBLANC O; GARBUS I; ECHENIQUE V

Oslo

Congreso; European Frontiers of Plant Reproduction Research; 2013

EU COST action FA0903 "Harnessing Plant Reproduction for Crop Improvement"

Apomixis in plants refers to a diverse group of developmental behaviors resulting in asexual reproduction through seeds. Apomictic individuals bypass both meiotic reduction and egg cell fertilization to produce offspring that are exact genetic replicas of the maternal plant. Given the established relationship between sexual and apomictic pathways, different models have been proposed to explain the occurrence of apomixis at the molecular level involving genetic and epigenetic mechanisms. Weeping lovegrass (Eragrostis curvula [Schrad.] Nees) is an apomictic perennial grass native to Southern Africa. The type of apomixis present in the E. curvula is pseudogamous diplospory. Meiotic stages are absent from the Eragrostis-type apomixis, and the megasporocyte undergoes only two rounds of mitotic division to form a non-reduced tetranucleated embryo sac with an egg, two synergids, and one polar nucleus. The E. curvula complex includes cytotypes with different ploidy levels (from 2x to 8x) that may undergo sexual reproduction, facultative apomixis or obligate apomixis. Diploid (2n = 2x = 20) plants are sexual and rare. Polyploids reproduce mainly by obligate apomixis, but sexual and facultative apomixis has also been reported. Since long time ago our group has been studying different aspects of the genetics and physiology of weeping lovegrass. There are recent evidences on the role played by certain proteins of the RdDM pathways involved in gametophytic apomixis expression, suggesting an epigenetic regulation of the trait. It was reported in maize that loss-of-function of dmt103 and dmt102 methyltransferases genes partially mimics apomictic developments. Something similar happens with the AGO104 protein. Loss-of-function in ago104, a maize homolog of ago9, also results in apomixis-like traits, giving rise to up to 70% of functional unreduced female gametes. These data suggest that methyltransferases deregulation plays a role on the establishment of apomixis. The aim of this work was to study the expression of genes associated to RdDM pathway in sexual and apomictic flowers and leaves of E. curvula plants. The BlastX algorithm was used to find the corresponding Eragrostis curvula RdDM genes using the ChromDB database. The phylogenetic analysis indicated that these genes group together in the same clade with the corresponding ones in Arabidopsis and maize. The dmt104, chr106, hdt104 and ago104 genes profiles were analysed using qRT-PCR in leaves and in different stages of reproductive tissues. Primers were designed on EST sequences from E. curvula and also on genes associated to RdDM pathway in Arabidopsis and maize. The expression studies indicated a decreased activity of all these four genes in the sexual genotypes, suggesting a high silencing status in the apomictic ones.