Natural variation in FLOWERING LOCUS C and FLOWERING LOCUS M underlies the weak temperature sensitivity of the Arabidopsis accession Ellershausen

Natural variants of key floral regulator genes underly the adaptation of plant populations to diverse environmental conditions. We identified Ellershausen (El-0) as an early flowering Arabidopsis (Arabidopsis thaliana) accession with decreased sensitivity to changes in temperature and photoperiod. Expression levels of FLOWERING LOCUS M (FLM), including its major splice variants FLM-β and FLM-δ, were dramatically lower in El-0 than in Col-0 or Killean (Kil-0) accessions at different temperatures. The first intron of FLM^El−0 contains a ∼5.7-kb LINE transposon insertion, as in Kil-0, together with several single-nucleotide polymorphisms. However, El-0 flowered earlier than Kil-0 at 23 °C or 16 °C under long-day conditions and at 23°C under short-day conditions. Introducing a genomic copy of FLM^Col−0 into El-0 moderately delayed flowering, suggesting that an additional player(s) is involved in the temperature-insensitive flowering of El-0. Accordingly, expression levels of FLOWERING LOCUS C (FLC) and MADS AFFECTING FLOWERING 5 (MAF5) were lower in El-0. Genome resequencing data revealed polymorphisms including deletions in FLC^El−0 and MAF5^El−0. β-Glucuronidase activity was weaker in pFLC^Col−0:gFLC^El−0-GUS transgenic seedlings than in pFLC^Col−0:gFLC^Col−0-GUS seedlings, suggesting that polymorphisms in FLC^El−0 result in lower FLC^El−0 transcript levels. Consistent with low FLC expression levels, El-0 plants did not flower earlier following vernalization. Our results suggest that natural variants of these repressor genes in El-0 may facilitate successful adaptation to relatively cooler climates.