A J-Domain Protein J3 Antagonizes ABI5-BINDING PROTEIN2 to Regulate CONSTANS Stability and Flowering Time

Area of Science:

• Plant Biology
• Molecular Genetics
• Developmental Biology

Background:

• CONSTANS (CO) is a key regulator of photoperiod-dependent flowering, controlling the expression of the florigen FT gene.
• The diurnal oscillation of CO protein abundance is regulated by daylength and the circadian clock.
• ABI5-BINDING PROTEIN2 (AFP2) has been identified as a repressor of CO expression, delaying flowering.

Purpose of the Study:

• To identify proteins interacting with AFP2.
• To elucidate the role of DNAJ HOMOLOG 3 (J3) in the regulation of flowering time and CO protein stability.
• To understand the molecular mechanism by which J3 influences photoperiod responses.

Main Methods:

• Yeast two-hybrid assays and co-immunoprecipitation to confirm protein interactions.
• Analysis of flowering time in Arabidopsis thaliana mutants (j3) and overexpression lines.
• Western blot analysis to assess CO protein abundance.
• Genetic analysis of double mutants (afp2 j3).

Main Results:

• DNAJ HOMOLOG 3 (J3) interacts with AFP2.
• The j3 mutant exhibits late flowering and reduced CO protein levels in long days.
• J3 overexpression accelerates flowering by stabilizing CO protein.
• J3 antagonizes AFP2's repression of CO, protecting CO from degradation and promoting FT expression.
• Overexpression of J3 reverses AFP2-induced late flowering, and the afp2 mutant phenotype is suppressed in the afp2 j3 double mutant.

Conclusions:

• J3 acts as a positive regulator of photoperiodic flowering in Arabidopsis thaliana.
• J3 fine-tunes FT gene expression by stabilizing CO protein through antagonizing AFP2 activity.
• This study reveals a novel mechanism coordinating CO stability and photoperiod responses.