The Microtubule-Associated Protein CsTON2 Interacts With CsTRM5 and CsSUN to Regulate Fruit Shape Development in Cucumber.

Fruit shape is an important external quality trait that directly determines the market value. Modification of fruit shape has emerged as a key focus in crop improvement, but the regulatory network of fruit shape specifications remains largely unknown. Here, we identified a short fruit mutant (sf5) that was caused by a C-to-T single nucleotide polymorphism (SNP) in TONNEAU2 (CsTON2), a microtubule-associated gene encoding the B subunit of protein phosphatase 2A (PP2A). Overexpression of CsTON2 in the sf5 background partially rescued the mutant phenotype, while knockout of CsTON2 led to severe developmental defects and dwarfism. We further demonstrated that CsTON2 physically interacts with CsTRM5 and CsSUN, two key regulators of fruit shape in cucumber. The SNP change of CsTON2 in sf5 mutant impairs the interaction with CsTRM5 and CsSUN, and decreases the protein stability of CsSUN. Genetic analyses revealed that CsTON2, CsTRM5 and CsSUN coordinately regulate fruit shape development by modulating cell division direction in cucumber. Therefore, our findings shed insights into the role of microtubule-associated protein complex in fruit shape determination and provide new gene targets for breeding cucumber varieties with favourable fruit shapes.