Functional Dissection of Auxin Response Factors in Regulating Tomato Leaf Shape Development

Area of Science:

• Plant Biology
• Molecular Biology
• Genetics

Background:

• The phytohormone auxin is crucial for plant growth and development.
• The tomato Aux/IAA protein SlIAA9 regulates leaf and fruit development, but its precise mechanism in leaf morphogenesis is unclear.
• Auxin signaling involves Aux/IAA repressors and auxin response factors (ARFs).

Purpose of the Study:

• To elucidate the molecular mechanism by which SlIAA9 and ARFs control tomato leaf complexity.
• To identify specific ARF proteins interacting with SlIAA9 and their role in leaf development.

Main Methods:

• Yeast two-hybrid (Y2H) assays to identify ARF interactors of SlIAA9.
• Expression profiling of the SlARF gene family.
• Pull-down and Bimolecular Fluorescence Complementation (BiFC) assays for in vitro and in vivo interaction validation.
• Virus-induced gene silencing (VIGS) to assess the function of identified SlARFs.
• Quantitative analysis of IAA content.
• Promoter binding assays (ChIP-qPCR implied) and gene expression analysis.

Main Results:

• Four ARF proteins (SlARF6A, SlARF8A, SlARF8B, SlARF24) were identified as SlIAA9 interactors.
• The 'entire' (e) mutation, affecting SlIAA9, altered the expression of multiple SlARFs.
• Silencing these four SlARFs in the 'e' mutant partially converted simple leaves to compound leaves.
• IAA content increased in VIGS-treated 'e' mutant plants.
• SlARF6A and SlARF24 directly bind to the SlPIN1 promoter, acting as transcriptional activators.

Conclusions:

• SlARFs play a critical role in regulating tomato leaf morphology, potentially by directly binding to auxin-responsive genes.
• SlARFs can influence leaf development independently of SlIAA9, suggesting complex regulatory roles in auxin signaling pathways.
• This study provides insights into the genetic regulation of leaf shape development mediated by auxin signaling.