Functional conservation of MtFPA, a nucleus-localized RNA-recognition motif-binding protein that regulates flowering time in Medicago truncatula

Abstract

The FLOWERING TIME CONTROL PROTEIN FPA (FPA) gene encodes an RNA recognition motif (RRM) domain protein and plays an important role in flowering time control. Flowering responds to environmental conditions and developmental regulation through a network of signaling pathways. However, a little is known about the functions of autonomous pathway genes in Medicago truncatula. Here, we characterized the M. truncatula FPA (MtFPA) gene expression profiling through quantitative RT-PCR analysis, cellular localization, and functional analyses in transgenic plants. We cloned the FPA gene of M. truncatula based on its sequence similarity with Arabidopsis thaliana FPA. The quantitative RT-PCR analysis of MtFPA expression patterns showed that the MtFPA transcripts accumulated ubiquitously in the roots, leaves, stems, flowers, and pods of M. truncatula. The confocal image analysis of the fusion protein MtFPA:GFP revealed that MtFPA was localized in the nucleus. To examine the function of MtFPA, the 35S::MtFPA transgenic plants were generated in the Arabidopsis late-flowering mutant background, fpa-2. The overexpression of MtFPA accelerated flowering under long day conditions compared to the non-transgenic plants. In MtFPA transgenic lines, the expression of AtFLC was down-regulated, whereas that of the floral integrators, AtFT and AtSOC1, was up-regulated as compared to the control plants. These results suggest that MtFPA is a functional orthologue of Arabidopsis and plays an important role in the regulation of flowering time in legumes, especially in M. truncatula.