Suppression of Late-Flowering and Semi-Dwarf Phenotypes in theArabidopsisClock Mutantlhy-12;cca1-101byphyBunder Continuous Light

Aug 9, 2011Plant signaling & behavior

How a light-sensing protein reduces late flowering and short growth in a plant clock mutant under constant light

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Abstract

Double mutations in LHY and CCA1 accelerated flowering under short days but delayed it under continuous light.

Mutations in LHY and CCA1 (lhy;cca1) primarily affect the GI-CO dependent flowering pathway.
Under continuous light, lhy;cca1 showed delayed flowering possibly due to the GI-CO independent pathway.
The late-flowering phenotype in lhy;cca1 was suppressed by mutations in SVP, FLC, and ELF3.
lhy;cca1 exhibited shorter hypocotyls and petioles under continuous light, although the underlying mechanisms remain unclear.
Two novel mutations, del1 and phyB-2511, were identified that suppress lhy;cca1 phenotypes under continuous light.
PhyB mutations appear to influence flowering time and organ elongation, potentially affecting downstream factors of the clock proteins.

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Photoperiodic flowering in Arabidopsis is controlled not only by floral activators such as GI, CO, and FT, but also by repressors such as SVP and FLC. Double mutations in LHY and CCA1 (lhy;cca1) accelerated flowering under short days, mainly by the GI-CO dependent pathway. In contrast, lhy;cca1 showed delayed flowering under continuous light (LL), probably due to the GI-CO independent pathway. This late-flowering phenotype was suppressed by svp, flc, and elf3. However, how SVP, FLC, and ELF3 mediate LHY/CCA1 and flowering time is not fully understood. We found that lhy;cca1 exhibited short hypocotyls and petioles under LL, but the molecular mechanism for these effects has not been elucidated. To address these questions, we performed a screen for mutations that suppress either or both of the lhy;cca1 phenotypes under LL, using two different approaches. We identified two novel mutations, a dominant (del1) and a recessive (phyB-2511) allele of phyB. The flowering times of single mutants of three phyB alleles, hy3-1, del1, and phyB-2511, are almost the same and earlier than those of wild-type plants. A similar level of acceleration of flowering time was observed in all three phyB mutants tested when combined with the late-flowering mutations co-2 and SVPox. However, the effect of phyB-2511 on lhy;cca1 was different from those by hy3-1 or del1. svp-3 did not strongly enhance the early-flowering phenotypes of phyB-2511 or del1. These results suggest that light signaling via PhyB may affect factors downstream of the clock proteins, controlling flowering time and organ elongation. phyB mutations with different levels of effects on lhy;cca1-dependent late flowering would be useful to determine a specific role for PHYB in the flowering pathway controlled by lhy;cca1 under LL.

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Suppression of Late-Flowering and Semi-Dwarf Phenotypes in theArabidopsisClock Mutantlhy-12;cca1-101byphyBunder Continuous Light

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