Regulatory function of EARLI1-LIKE HYBRID PROLINE-RICH PROTEIN1 in the floral transition of Arabidopsis thaliana

The plasma membrane- and endoplasmic reticulum-localized proteins encoded by the EARLI1 (EARLY ARABIDOPSIS ALUMINUM INDUCED 1) subfamily of genes contain a signal peptide, a proline-rich domain and an eight-cysteine motif. We previously showed that knockdown of EARLI1 subfamily genes in the late-flowering background of Col-FRI-Sf2 accelerates flowering time, suggesting that EARLI1 genes participate in maintenance of vegetative growth and prevention of premature reproductive growth. We show here that ELHyPRP1 (EARLI1-LIKE HYBRID PROLINE-RICH PROTEIN 1, AT4G12490), a member of this subfamily, is induced by environmental factors such as cold and long-day photoperiod. Detailed analyses with RNA interference and overexpressing lines demonstrated that modulation of ELHyPRP1 can affect the expression of photoperiod, vernalization, gibberellin, age, and autonomous flowering pathway genes. When ELHyPRP1 and other EARLI1 subfamily genes were silenced by RNA interference, most genes participating in the promotion of flowering were activated, while suppressors of the floral transition were repressed. Downregulation of ELHyPRP1 leads to increased expression of the flowering time genes FT and SOC1, and enhanced circadian expression patterns of genes associated with the promotion of the floral transition. Together with the silencing of ELHyPRP1, the flowering repressor FLC and the GA signalling repressor RGA were inhibited. ELHyPRP1 transgenic tobacco plants displayed late-flowering phenotypes and their flowering time was remarkably delayed in comparison to the wild-type Qinyan 95 tobacco plants grown under long-day photoperiod. These results indicate that ELHyPRP1 may be involved in balancing biomass accumulation and seed proliferation.