SlMYC2 promotes SlLBD40-mediated cell expansion in tomato fruit development

Area of Science:

• Plant Molecular Biology
• Plant Physiology

Background:

• Lateral organ boundary domain (LBD) proteins are plant-specific transcription factors involved in growth and stress responses, with limited research on subfamily II.
• SlMYC2, a key regulator of jasmonic acid signaling, is highly expressed in tomato fruit and influences ripening and disease resistance, but its role in fruit expansion is unknown.

Purpose of the Study:

• To investigate the role of SlLBD40, a subfamily II LBD gene, in tomato fruit expansion.
• To elucidate the interaction between SlLBD40 and SlMYC2 in regulating fruit size.

Main Methods:

• Gene overexpression and knockout in tomato plants.
• Analysis of mesocarp cell expansion and fruit growth.
• Yeast two-hybrid assays and co-immunoprecipitation to study protein interactions.
• Promoter binding assays and gene expression analysis (qRT-PCR).

Main Results:

• Overexpression of SlLBD40 promoted fruit growth by enhancing mesocarp cell expansion; SlLBD40 knockout inhibited this process.
• SlMYC2 knockout significantly reduced fruit cell expansion, indicating its essential role.
• SlLBD40's function in cell expansion is dependent on SlMYC2 expression.
• SlLBD40 and SlMYC2 co-expression synergistically activated the expansin gene SlEXPA5, increasing fruit size.
• SlLBD40 interacted with SlMYC2, enhancing its stability and abundance.
• SlMYC2 directly activated SlLBD40 expression, which is crucial for SlLBD40-mediated fruit expansion.

Conclusions:

• SlLBD40 and SlMYC2 form a regulatory complex that promotes tomato fruit expansion.
• This interaction enhances SlEXPA5 expression, leading to increased cell expansion and fruit size.
• The study reveals a novel molecular mechanism controlling fruit growth through the SlMYC2-SlLBD40 pathway.