Abstract
BackgroundPlants must integrate complex signals from environmental and endogenous cues to fine-tune the timing of flowering. Low temperature is one of the most common environmental stresses that affect flowering time; however, molecular mechanisms underlying the cold temperature regulation of flowering time are not fully understood.Methodology/Principal FindingsWe report the identification of a novel regulator, LONG VEGETATIVE PHASE 1 (LOV1), that controls flowering time and cold response. An Arabidopsis mutant, long v egetative phase 1-1D (lov1-1D) showing the late-flowering phenotype, was isolated by activation tagging screening. Subsequent analyses demonstrated that the phenotype of the mutant resulted from the overexpression of a NAC-domain protein gene (At2g02450). Both gain- and loss-of-function alleles of LOV1 affected flowering time predominantly under long-day but not short-day conditions, suggesting that LOV1 may act within the photoperiod pathway. The expression of CONSTANS (CO), a floral promoter, was affected by LOV1 level, suggesting that LOV1 controls flowering time by negatively regulating CO expression. The epistatic relationship between CO and LOV1 was consistent with this proposed regulatory pathway. Physiological analyses to elucidate upstream signalling pathways revealed that LOV1 regulates the cold response in plants. Loss of LOV1 function resulted in hypersensitivity to cold temperature, whereas a gain-of-function allele conferred cold tolerance. The freezing tolerance was accompanied by upregulation of cold response genes, COLD-REGULATED 15A (COR15A) and COLD INDUCED 1 (KIN1) without affecting expression of the C-repeat-binding factor/dehydration responsive element-binding factor 1 (CBF/DREB1) family of genes.ConclusionsOur study shows that LOV1 functions as a floral repressor that negatively regulates CO expression under long-day conditions and acts as a common regulator of two intersecting pathways that regulate flowering time and the cold response, respectively. Our results suggest an overlapping pathway for controlling cold stress response and flowering time in plants.
Highlights
Timing of the developmental transition to the reproductive phase is very important for plants to ensure successful reproduction and requires the proper perception and processing of a variety of stimuli
This mutant, which we denoted as long vegetative phase 1-1D, flowered with 26.6 leaves under long days, whereas wild-type plants flowered with 15.5 leaves (Figure 1A)
KIN1 expression levels remained unaltered in lov1-4 mutants, suggesting that LONG VEGETATIVE PHASE 1 (LOV1) may not be essential for the expression of KIN1. These results suggest that the changed sensitivity of lov1 mutants to cold temperature is, at least partially, conferred by the altered expression of COLD-REGULATED 15A (COR15A) and KIN1 genes and may be regulated by means of one of several CBF/ DREB1-independent signalling pathways in the cold response [40]
Summary
Timing of the developmental transition to the reproductive phase is very important for plants to ensure successful reproduction and requires the proper perception and processing of a variety of stimuli. In Arabidopsis, at least four major floral promotion pathways are known to mediate signalling from the different cues: the photoperiod, vernalization, autonomous and gibberellin (GA) pathways [1] Of these pathways, the photoperiod pathway plays an important role in controlling the timing of the developmental transition to flowering in Arabidopsis. Subsequent analyses demonstrated that the phenotype of the mutant resulted from the overexpression of a NAC-domain protein gene (At2g02450) Both gain- and loss-of-function alleles of LOV1 affected flowering time predominantly under long-day but not short-day conditions, suggesting that LOV1 may act within the photoperiod pathway. Our study shows that LOV1 functions as a floral repressor that negatively regulates CO expression under long-day conditions and acts as a common regulator of two intersecting pathways that regulate flowering time and the cold response, respectively. Our results suggest an overlapping pathway for controlling cold stress response and flowering time in plants
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