The phytochrome-interacting vascular plant one-zinc finger1 and VOZ2 redundantly regulate flowering in Arabidopsis.

The timing of the transition to flowering in plants is regulated by various environmental factors, including daylength and light quality. Although the red/far-red photoreceptor phytochrome B (phyB) represses flowering by indirectly regulating the expression of a key flowering regulator, FLOWERING LOCUS T (FT), the mechanism of phyB signaling for flowering is largely unknown. Here, we identified two Arabidopsis thaliana genes, VASCULAR PLANT ONE-ZINC FINGER1 (VOZ1) and VOZ2, which are highly conserved throughout land plant evolution, as phyB-interacting factors. voz1 voz2 double mutants, but neither single mutant, showed a late-flowering phenotype under long-day conditions, which indicated that VOZ1 and VOZ2 redundantly promote flowering. voz1 voz2 mutations suppressed the early-flowering phenotype of the phyB mutant, and FT expression was repressed in the voz1 voz2 mutant. Green fluorescent protein-VOZ2 signal was observed in the cytoplasm, and interaction of VOZ proteins with phyB was indicated to occur in the cytoplasm under far-red light. However, VOZ2 protein modified to localize constitutively in the nucleus promoted flowering. In addition, the stability of VOZ2 proteins in the nucleus was modulated by light quality in a phytochrome-dependent manner. We propose that partial translocation of VOZ proteins from the cytoplasm to the nucleus mediates the initial step of the phyB signal transduction pathway that regulates flowering.

Transcriptome profiling of Lotus japonicus roots during arbuscular mycorrhiza development and comparison with that of nodulation.

To better understand the molecular responses of plants to arbuscular mycorrhizal (AM) fungi, we analyzed the differential gene expression patterns of Lotus japonicus, a model legume, with the aid of a large-scale cDNA macroarray. Experiments were carried out considering the effects of contaminating microorganisms in the soil inoculants. When the colonization by AM fungi, i.e. Glomus mosseae and Gigaspora margarita, was well established, four cysteine protease genes were induced. In situ hybridization revealed that these cysteine protease genes were specifically expressed in arbuscule-containing inner cortical cells of AM roots. On the other hand, phenylpropanoid biosynthesis-related genes for phenylalanine ammonia-lyase (PAL), chalcone synthase, etc. were repressed in the later stage, although they were moderately up-regulated on the initial association with the AM fungus. Real-time RT-PCR experiments supported the array experiments. To further confirm the characteristic expression, a PAL promoter was fused with a reporter gene and introduced into L. japonicus, and then the transformants were grown with a commercial inoculum of G. mosseae. The reporter activity was augmented throughout the roots due to the presence of contaminating microorganisms in the inoculum. Interestingly, G. mosseae only colonized where the reporter activity was low. Comparison of the transcriptome profiles of AM roots and nitrogen-fixing root nodules formed with Mesorhizobium loti indicated that the PAL genes and other phenylpropanoid biosynthesis-related genes were similarly repressed in the two organs.