Abstract
BackgroundCorrect timing of flowering is critical for plants to produce enough viable offspring. In Arabidopsis thaliana (Arabidopsis), flowering time is regulated by an intricate network of molecular signaling pathways. Arabidopsis srr1–1 mutants lacking SENSITIVITY TO RED LIGHT REDUCED 1 (SRR1) expression flower early, particularly under short day (SD) conditions (1). SRR1 ensures that plants do not flower prematurely in such non-inductive conditions by controlling repression of the key florigen FT. Here, we have examined the role of SRR1 in the closely related crop species Brassica napus.ResultsArabidopsis SRR1 has five homologs in Brassica napus. They can be divided into two groups, where the A02 and C02 copies show high similarity to AtSRR1 on the protein level. The other group, including the A03, A10 and C09 copies all carry a larger deletion in the amino acid sequence. Three of the homologs are expressed at detectable levels: A02, C02 and C09. Notably, the gene copies show a differential expression pattern between spring and winter type accessions of B. napus. When the three expressed gene copies were introduced into the srr1–1 background, only A02 and C02 were able to complement the srr1–1 early flowering phenotype, while C09 could not. Transcriptional analysis of known SRR1 targets in Bna.SRR1-transformed lines showed that CYCLING DOF FACTOR 1 (CDF1) expression is key for flowering time control via SRR1.ConclusionsWe observed subfunctionalization of the B. napus SRR1 gene copies, with differential expression between early and late flowering accessions of some Bna.SRR1 copies. This suggests involvement of Bna.SRR1 in regulation of seasonal flowering in B. napus. The C09 gene copy was unable to complement srr1–1 plants, but is highly expressed in B. napus, suggesting specialization of a particular function. Furthermore, the C09 protein carries a deletion which may pinpoint a key region of the SRR1 protein potentially important for its molecular function. This is important evidence of functional domain annotation in the highly conserved but unique SRR1 amino acid sequence.
Highlights
Correct timing of flowering is critical for plants to produce enough viable offspring
An important FLOWERING LOCUS T (FT) repressor in this transcriptional landscape is the MADS box transcription factor FLOWERING LOCUS C (FLC), which has an important role as a repressor of flowering in unfavorable conditions, as its expression level is reduced by extended periods of cold [14, 15]
Gene sequence analysis shows that the five Bna.SENSITIVITY TO RED LIGHT REDUCED 1 (SRR1) copies can be divided into two groups, based on their predicted amino acid sequence
Summary
Correct timing of flowering is critical for plants to produce enough viable offspring. Onset of flowering is tightly controlled by a network of signals originating from developmental, as well as environmental signaling pathways [2,3,4]. FKF1 represses the activity of CDF transcription factors, which have a repressive role on CO expression [11,12,13]. This allows accumulation of CO transcript in the afternoon and CO protein expression. Transcription of FT is tightly regulated by both promotive and repressive elements that integrate signals from various environmental and developmental signaling pathways [2]. An important FT repressor in this transcriptional landscape is the MADS box transcription factor FLOWERING LOCUS C (FLC), which has an important role as a repressor of flowering in unfavorable conditions, as its expression level is reduced by extended periods of cold [14, 15]
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