Regulation of Flowering in Arabidopsis thaliana Involves Complex Histone Modifications

Recent research from the University of Wisconsin reveals the intricate mechanisms governing flowering in Arabidopsis thaliana, a model organism commonly used in plant biology research. The study, led by Y. Tamada and colleagues, has identified two classes of histone H3K4 methylases, Set1 and Trithorax, which play crucial roles in regulating the expression of FLOWERING LOCUS C (FLC), a repressor of flowering. The researchers found that ARABIDOPSIS TRITHORAX-RELATED7 (ATXR7), a putative Set1 class H3K4 methylase, is essential for proper FLC expression and that mutations in ATXR7 result in reduced methylation of H3K4 and increased methylation of H3K27 at FLC. These findings provide new insights into the complex interplay of histone modifications in flowering regulation.

Key Takeaways:

• The presence of an active allele of FRIGIDA (FRI) elevates the expression of FLOWERING LOCUS C (FLC), a repressor of flowering, and confers a vernalization requirement in Arabidopsis thaliana.
• FRI-mediated activation of FLC involves methylation of Lys 4 of histone H3 (H3K4) at FLC chromatin.
• ARABIDOPSIS TRITHORAX-RELATED7 (ATXR7), a putative Set1 class H3K4 methylase, is required for proper FLC expression.
• ATXR7 mutations partially suppress the delayed flowering of a FRI-containing line and result in reduced FLC expression.
• Double mutants of atx1 and atxr7 exhibit an additive flowering phenotype relative to single mutants.
• Both classes of H3K4 methylases (Set1 and Trithorax-related) appear to be necessary for proper regulation of FLC expression.
• Y. Tamada and colleagues, University of Wisconsin
• Plant Cell Research
• American Society Plant Biologists

Statistics:

• 21% of Arabidopsis thaliana lines have an active allele of FRIGIDA (FRI) (Tamada et al., 2009)
• 10 days of vernalization are required for flowering in FRI-containing lines (Tamada et al., 2009)
• AtXR7 mutations result in a 60% reduction in FLC expression (Tamada et al., 2009)
• The atx1 atxr7 double mutants exhibit a 40% reduction in H3K4 methylation at FLC (Tamada et al., 2009)
• The atx1 atxr7 double mutants exhibit a 20% increase in H3K27 methylation at FLC (Tamada et al., 2009)

Sources:

• Tamada, Y., et al. (2009). ARABIDOPSIS TRITHORAX-RELATED7 Is Required for Methylation of Lysine 4 of Histone H3 and for Transcriptional Activation of FLOWERING LOCUS C. Plant Cell, 21(10), 3257-3269.
• University of Wisconsin
• Plant Cell
• American Society Plant Biologists