Life cycle of flowering plants alternates between a dominating sporophytic and a shorter gametophytic phase, which is represented by pollen grains and embryo sac in male and female reproductive organs, respectively. Anther is a multilayered male reproductive organ, composed of four somatic wall layers surrounding the gametophytic cells, microspores. Precise control of differentiation and development of each cell type is crucial for proper development and dispersal of the male gametophyte. The normal developmental progression through different stages obligates cooperative functional interactions between gametophytic and sporophytic tissues. Various regulatory controls at transcription, translation and posttranslational levels are known to be operative during reproductive development. Molecular genetics studies have revealed a large number of genes regulating different aspects of development, including stamen meristem specification, early anther development, differentiation and maturation of pollen grains. However, the molecular mechanisms that regulate the transition from the Sporophytic to the Gametophytic phase (S2G) are still elusive.
Using a previously generated in-house transcriptomics data comprising of 25 stages/tissues of vegetative and reproductive development in rice, we identified specific up-regulation of genes involved in the regulation of transcription, signal transduction and protein metabolism during S2G transition in anthers. Of the genes involved in protein metabolism machinery, 23 were found to code for F-box class of proteins that are known for their involvement in the E3 ligase (SCF) complex that ubiquitinates specific proteins destined for degradation by the 26S proteasome complex by interaction with SKP-like genes. We also identified five meiotic stage-specific Oryza sativa SKP-like genes (OSKs) in rice. One-to-one interaction analyses with these co-expressing SKP-like genes by yeast-two-hybrid (Y2H) and bi-molecular fluorescence complementation (BiFC) assays have confirmed that FBDUF27 interacts positively with OSK22 and OSK19, whereas FBDUF29 interacts only with OSK22. Besides, some weak interactions were also observed amongst other F-box and OSK proteins. Based on these investigations three genes, FBDUF27, FBX350 and OSK22, were selected for functional characterization by using knock-down and ectopic expression approaches in transgenic rice system.
Department of Plant Molecular Biology, University of Delhi South Campus, New Delhi-110021, India