Post-translational regulation of SHORT VEGETATIVE PHASE as a major mechanism for thermoregulation of flowering.

In contrast to our extensive knowledge of vernalization, we know relatively little about the regulation of ambient temperature-responsive flowering. Recent reports revealed that flowering locus M (FLM) and short vegetative phase (SVP) regulate high ambient temperature-responsive flowering through two different mechanisms: degradation of SVP protein and formation of a non-functional SVP-FLM-δ complex. To investigate further the mechanism of thermoregulation of flowering, we performed real-time quantitative polymerase chain reaction (RT-qPCR) and in vitro pull-down assays. We found that FLM-ß and FLM-δ transcripts show similar absolute levels at different temperatures. Also, His-SVP protein bound to the GST-FLM-ß or -δ proteins with similar binding intensities. These results suggest that functional SVP-FLM-ß and non-functional SVP-FLM-δ complexes form similarly at warmer temperatures, thus indicating that post-translational regulation of SVP functions as a major mechanism for thermoregulation in flowering.

Role of SEPALLATA3 (SEP3) as a downstream gene of miR156-SPL3-FT circuitry in ambient temperature-responsive flowering.

SEPALLATA3 (SEP3) is important in determining flowering time as well as floral organ identity. Although much is known about the regulation of floral organ identity by SEP3, its role as a downstream gene of FLOWERING LOCUS T (FT) for the regulation of ambient temperature-responsive flowering is poorly understood. Here, we show that SEP3 as a downstream gene of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE3 (SPL3) and FT modulates the flowering time in response to different ambient temperatures. SEP3 overexpression showed temperature-insensitive flowering at 23°C and 16°C. This suggests that altered SEP3 activity affects ambient temperature-responsive flowering. However, a lesion in SEP3 did not obviously affect ambient temperature-responsive flowering. SEP3 expression was affected by altered SPL3 and FT activities in the leaf and shoot apical regions at different temperatures. These results suggest that the miR156-SPL3-FT circuitry directly or indirectly regulates SEP3 expression for the regulation of ambient temperature-responsive flowering in Arabidopsis.