B-box transcription factor 28 regulates flowering by interacting with constans

Area of Science:

• Plant Molecular Biology
• Genetics
• Developmental Biology

Background:

• B-box transcription factors (BBXs) are key regulators of various plant processes, including flowering time.
• Arabidopsis thaliana has 32 BBX proteins classified into five groups, with limited knowledge on Group V members.
• Understanding BBX functions, particularly Group V, is essential for deciphering plant development.

Purpose of the Study:

• To investigate the function of B-box transcription factor 28 (BBX28), a Group V member, in regulating flowering time.
• To elucidate the molecular mechanism by which BBX28 interacts with Constans (CO) and Flowering Locus T (FT).

Main Methods:

• Identification and characterization of BBX28 in Arabidopsis.
• Analysis of BBX28 overexpression and mutant phenotypes under long day conditions.
• Investigation of the interaction between BBX28 and CO using molecular assays.
• Assessing the effect of BBX28 on CO binding to the FT locus and its transcriptional activity.

Main Results:

• Overexpression of BBX28 resulted in late flowering and decreased FT transcription, while bbx28 mutants showed early flowering under long days.
• BBX28 directly interacts with CO, reducing CO's recruitment to the FT locus without altering CO's transcriptional activity.
• N-terminal cysteines, including those in the B-box domain of BBX28, are critical for CO heterodimerization and FT activation.
• Genetic evidence confirmed that BBX28 overexpression's late-flowering phenotype is suppressed by CO ectopic expression.

Conclusions:

• BBX28 functions in conjunction with CO and FT to negatively regulate flowering time in Arabidopsis under long days.
• The N-terminal conserved cysteines of BBX28 play a pivotal role in this regulatory mechanism.
• BBX28 represents a novel component in the complex network controlling plant flowering.