FvMYB79 Positively Regulates Strawberry Fruit Softening via Transcriptional Activation of FvPME38

Strawberry is a soft fruit with short postharvest life, due to a rapid loss of firmness. Pectin methylesterase (PME)-mediated cell wall remodeling is important to determine fruit firmness and softening. Previously, we have verified the essential role ofFvPME38in regulation of PME-mediated strawberry fruit softening. However, the regulatory network involved in PME-mediated fruit softening is still largely unknown. Here, we identified an R2R3-type MYB transcription factor FvMYB79, which activates the expression level ofFvPME38, thereby accelerating fruit softening. During fruit development,FvMYB79co-expressed withFvPME38, and this co-expression pattern was opposite to the change of fruit firmness in the fruit of ‘Ruegen’ which significantly decreased during fruit developmental stages and suddenly became very low after the color turning stage. Via transient transformation, FvMYB79 could significantly increase the transcriptional level ofFvPME38, leading to a decrease of firmness and acceleration of fruit ripening. In addition, silencing ofFvMYB79showed an insensitivity to ABA-induced fruit ripening, suggesting a possible involvement ofFvMYB79in the ABA-dependent fruit softening process. Our findings suggest FvMYB79 acts as a novel regulator during strawberry ripening via transcriptional activation ofFvPME38, which provides a novel mechanism for improvement of strawberry fruit firmness.Keywords:fruit softening;strawberry;FvMYB79;FvPME38