GA2ox1-1 modulates bioactive gibberellin levels to regulate the RGL3-MYB169 pathway in pear stone cell formation

Area of Science:

• Plant Biology
• Molecular Biology
• Fruit Science

Background:

• Stone cells in pear (Pyrus spp.) fruit significantly impact quality, but the underlying hormonal regulation is unclear.
• Plant hormones, particularly gibberellins (GAs), are known to influence fruit development, yet their specific role in stone cell lignification is poorly understood.
• Understanding stone cell formation mechanisms is crucial for improving pear fruit quality through cultivar selection or targeted interventions.

Purpose of the Study:

• To investigate the role of plant hormones, specifically gibberellins (GAs), in the formation and lignification of stone cells in pear fruit.
• To identify key genes and regulatory pathways involved in GA-mediated stone cell development using co-expression network analysis.
• To elucidate the molecular mechanism by which GA influences lignin biosynthesis and stone cell abundance in pears.

Main Methods:

• RNA sequencing (RNA-seq) data from 206 pear (Pyrus pyrifolia) cultivars were analyzed for co-expression networks linking hormone biosynthesis genes with stone cell regulators.
• Gibberellin (GA) 2-oxidase 1-1 (GA2ox1-1) gene expression and localization were validated using RNA in situ hybridization.
• Functional validation of GA2ox1-1 was performed in pear fruit, callus, and Arabidopsis (Arabidopsis thaliana) to assess its effect on lignin content and active GA levels.
• Protein-protein interactions and regulatory mechanisms were investigated, focusing on the DELLA protein REPRESSOR of ga1-3 Like 3 (RGL3) and Myeloblastosis transcription factor MYB169 in the GA signaling pathway.

Main Results:

• Co-expression analysis identified GA2ox1-1 as a key gene significantly correlated with stone cell content, showing increased expression during development and specific localization to stone cells.
• Overexpression of GA2ox1-1 led to reduced lignin content and lower active GA levels in pear tissues and Arabidopsis.
• The DELLA protein RGL3 was identified as a negative regulator of lignin biosynthesis, interacting with and suppressing the transcription factor MYB169.
• GA signaling relieved RGL3-mediated suppression of MYB169, leading to increased lignin biosynthesis and enhanced stone cell deposition.

Conclusions:

• Gibberellin (GA) plays a critical role in regulating stone cell formation in pears, primarily by modulating lignin biosynthesis.
• A novel regulatory pathway involving the interaction between RGL3 and MYB169, modulated by GA levels, controls lignin deposition in stone cells.
• This research provides fundamental insights into the molecular mechanisms governing stone cell development, offering potential strategies to improve pear fruit quality by manipulating stone cell content.