Exploring PLT gene family for insights into parthenogenesis regulation in Eragrostis curvula

Abstract

Apomixis is an asexual reproduction regulated by three mechanisms that together generate viable seeds genetically identical to the mother. These mechanisms are, 1) apomeiosis (lack of female meiosis), 2)parthenogenesis (embryo development without egg cell fertilization) and 3) pseudogamy (single fertilization ofthe polar nuclei). Depending on the species, parthenogenesis was found regulated by different genes. In Taraxacum officinale, two unlinked dominant loci control diplospory (DIP) and fertilization independent development of an embryo from the egg cell (PAR). InPennisetum squamulatum and Cenchus ciliaris BABYBOOM (BBM)-like genes were identified as candidates for parthenogenesis. Ectopic expression of these genes using egg cell specific promoter in rice showed autonomous embryo development. In normal developmentBBM genes were found expressed during fertilization triggered by the pollen. BBM genes belong to the plethora(PLT) family of transcription factors characterized by two conserved APETALA2 (AP2) binding domains and abbm-1 domain with functional implications for somatic embryogenesis.Eragrostis curvula is a diplosporous apomictic grass used as model for the study of apomixis. Several genetic and epigenetic resources have beendeveloped for this grass; however, the molecular regulation of parthenogenesis was not characterized yet. Inorder to test if parthenogenesis is also regulated by BBM in E. curvula a genome wide identification of PLTfamily was conducted. In this way the E. curvula genome annotation was used to identify genes with AP2domains. Further phylogenetic analysis showed that the ten PLT genes present in rice are also present in E. curvula. PLT5 and PLT6, which are BBM3 and BBM1 respectively, were analyzed in detail to characterize theirfunction in E. curvula. Specific PCR primers designed for these genes showed promising results since theexpression patterns shows similarities with rice. Moreover, furthermore cloning and sequencing of PLT5 andPLT6 from genotypes contrasting in the reproductive mode showed structural differences both at the genomic and transcript levels. Finally, we are testing if the expression of these genes is triggered by the pollen and canled to the autonomous embryo development in E. curvula.