Small GTP binding protein, Rab GTPases are a large family of proteins with a variety of regulatory functions in membrane traffic and development. Previously, we characterized OsRab11, which in concert with OsGAP1 and OsGDI3 regulates vesicular trafficking from the trans-Golgi network (TGN) to the plasma membrane or vacuole. To further elucidate the physiological function of OsRab11 in plants, we performed yeast two-hybrid screens using OsRab11 as bait. OsOPR8 was isolated and shown to interact with OsRab11. A co-immunoprecipitation assay confirmed this interaction. The green fluorescent protein-OsOPR8 fusion product was targeted to the cytoplasm and peroxisomes of protoplasts from Arabidopsis thaliana. OsOPR8 exhibited NADPH-dependent reduction activity when 2-cyclohexen-1-one (CyHE) and 12-oxophytodienoic acid (OPDA) were supplied as possible substrates. Interestingly, NADPH oxidation by OsOPR8 was increased when wild-type OsRab11 or the constitutively active form of OsRab11 (Q78L) were included in the reaction mix, but not when the dominant negative form of OsRab11 (S28N) was included. OsRab11 was expressed broadly in plants and both OsRab11 and OsOPR8 were induced by jasmonic acid (JA) and elicitor treatments. Overexpressed OsRab11 transgenic plants showed resistance to pathogens through induced expression of JA-responsive genes. In conclusion, OsRab11 may be required for JA-mediated defense signaling by activating the reducing activity of OsOPR8.

In some plant species, prolonged exposure to low temperature during the winter season is necessary to acquire the competence to flower in the following spring. This process, known as vernalization, is an epigenetic change in which a mitotically stable change of the developmental potential of the meristem (competence to flower) is maintained even in the absence of the inducing signal (prolonged cold exposure). In Arabidopsis, vernalization results in stable epigenetic repression of a potent floral repressor, FLOWERING LOCUS C (FLC). Increased enrichment of Polycomb Repressive Complex 2 (PRC2) and trimethylated Histone H3 Lys 27 (H3K27me3) at FLC chromatin is necessary for the stable maintenance of FLC repression by vernalization. A long intronic noncoding RNA (termed as COLDAIR) is required for the vernalization-mediated epigenetic repression of FLC. COLDAIR physically associates with a component of PRC2 and targets PRC2 to FLC. COLDAIR is required for establishing stable repressive chromatin at FLC through its interaction with PRC2. In addition, floral integrator genes are targets of PRC2 complex, resulting in delayed flowering time through repression mechanism of PRC2 complex. Recently another long non-coding RNA was isolated from floral integrator gene and characterized the function of this long non coding RNA.

Heterotrimeric G proteins, consisting of Gα, Gβ and Gγ subunits, play important roles in plant development and cell signaling. In Arabidopsis, in addition to one prototypical G protein a subunit gene, GPA1, there are three extra-large G proteins, XLG1, XLG2, and XLG3 of largely unknown function. Yeast two-hybrid library screening and in vitro protein pull-down assays revealed that XLG2 interacts with the nuclear protein RELATED TO VERNALIZATION1 (RTV1). A mutant XLG2 that lacks GTP binding does not interact with RTV1, suggesting the dependence of this protein interaction on the G-protein cycle. Electrophoretic mobility shift assays show that RTV1 binds to DNA in vitro in a non-sequence specific manner and that GTP-bound XLG2 promotes the DNA binding activity of RTV1. Overexpression of RTV1 results in early flowering. Combined overexpression of XLG2 and RTV1 enhances this early flowering phenotype, and elevates expression of the floral pathway integrator genes, FT and SOC1, but does not repress expression of the floral repressor, FLC. Chromatin immunoprecipitation assays show that XLG2 increases RTV1 binding to FT and SOC1 promoters. Thus, a Ca2+-dependent Gprotein, XLG2, promotes RTV1 DNA binding activity for a subset of floral integrator genes, and contributes to floral transition.