Floral transition, the change from vegetative growth to reproductive development, is dramatic in flowering plants. Here, we show that one subgroup III member of the B-box (BBX) family, BBX17, is a repressor of floral transition under long-day conditions. BBX17 contains a B-box domain and a CCT domain. Although the phenotype of the BBX17 loss-of-function plants was comparable to that of wild-type plants, BBX17-overexpression plants displayed a delayed-flowering phenotype under long-day conditions. The delayed-flowering phenotype was not the result of an altered CONSTANS (CO) expression level but rather the repression of the FLOWERING LOCUS T (FT) expression level. BBX17 physically associated with CO and repressed its ability to control FT expression. Furthermore, the BBX17 protein degraded in the dark, but irradiating seedlings with white, blue, red or far-red light stabilized the BBX17 level. We also proved that the degradation of BBX17 was via 26S proteasome and requires COP1. Thus, BBX17 acts as a key factor in the CO–FT regulatory system to control Arabidopsis thaliana flowering.

Background: The TGACG-binding (TGA) family has 10 members that play vital roles in Arabidopsis thaliana defense responses and development. However, their involvement in controlling flowering time remains largely unknown and requires further investigation. Results: To study the role of TGA7 during floral transition, we first investigated the tga7 mutant, which displayed a delayed-flowering phenotype under both long-day and short-day conditions. We then performed a flowering genetic pathway analysis and found that both autonomous and thermosensory pathways may affect TGA7 expression. Furthermore, to reveal the differential gene expression profiles between wild-type (WT) and tga7, cDNA libraries were generated for WT and tga7 mutant seedlings at 9 days after germination. For each library, deep-sequencing produced approximately 6.67 Gb of high-quality sequences, with the majority (84.55 %) of mRNAs being between 500 and 3,000 nt. In total, 325 differentially expressed genes were identified between WT and tga7 mutant seedlings. Among them, four genes were associated with flowering time control. The differential expression of these four flowering-related genes was further validated by qRT-PCR. Conclusions: Among these four differentially expressed genes associated with flowering time control, FLC and MAF5 may be mainly responsible for the delayed-flowering phenotype in tga7, as TGA7 expression was regulated by autonomous pathway genes. These results provide a framework for further studying the role of TGA7 in promoting flowering.

Phosphorus nutrition has been known to influence floral transition in plants for a long time, but the underlying mechanism is unclear. Arabidopsis PHOSPHATE1 (PHO1) plays a critical role in phosphate translocation from roots to shoots, but whether and how it regulates floral transition is unknown. Here, we show that knockout mutation of PHO1 delays flowering under both long-day and short-day conditions. The late flowering of pho1 mutants can be partially rescued by Pi supplementation in rosettes or shoot apices. Grafting assay indicates that the late flowering of pho1 mutants is resulted from impaired phosphate translocation from roots to shoots. Knockout mutation of SPX1 and SPX2, two negative regulators of phosphate starvation response, partially rescues the late flowering of pho1 mutants. PHO1 is epistatic to PHO2, a negative regulator of PHO1, in flowering time regulation. Loss of PHO1 represses the expression of some floral activators, including FT encoding florigen, and induces the expression of some floral repressors in shoots. Genetic analyses indicate that at least jasmonic acid signaling is partially responsible for the late flowering of pho1 mutants. In addition, we find rice PHO1;2, the homology of PHO1, plays a similar role in floral transition. These results suggest that PHO1 integrates phosphorus nutrition and flowering time and could be used as a potential target in modulating phosphorus nutrition-mediated flowering time in plants.

A short-root rice mutant was isolated from an ethyl methane sulfonate-mutagenized library. From map-based cloning strategy, a point mutation, resulting in an amino acid change from proline to leucine, was identified in the fourth exon of a glutamyl-tRNA (Gln) amidotransferase B subunit family protein (OsGatB, LOC_Os11g34210). This gene is an ortholog of Arabidopsis GatB and yeast PET112. GatB is a subunit of tRNA-dependent amidotransferase (AdT), an essential enzyme involved in Gln-tRNAGln synthesis in mitochondria. Although previous studies have described that cessation in mitochondrial translation is lethal at very early developmental stages in plants, this point mutation resulted in a non-lethal phenotype of smaller root meristem and shorter root cell length. In the root, OsGatB was predominantly expressed in the root tip and played an important role in cell division and elongation there. OsGatB was localized in the mitochondria, and mitochondrial structure and function were all affected in Osgatb root tip cells.