Flavonols improve thermotolerance in tomato pollen during germination and tube elongation by maintaining ROS homeostasis

Elevated temperatures impair pollen performance and reproductive success, resulting in lower crop yields. The Solanum lycopersicum anthocyanin reduced (are) mutant has a FLAVANONE 3 HYDROXYLASE (F3H) gene mutation resulting in impaired synthesis of flavonol antioxidants. The are mutant has reduced pollen performance and seed set relative to the VF36 parental line, which is accentuated at elevated temperatures. Transformation of are with the wild-type F3H gene, or chemical complementation with flavonols, prevented temperature-dependent ROS accumulation in pollen and reversed ares reduced viability, germination, and tube elongation to VF36 levels. VF36 transformed with an F3H overexpression construct prevented temperature driven ROS increases and impaired pollen performance, revealing thermotolerance results from elevated flavonol synthesis. Although stigmas of are had reduced flavonols and elevated ROS, the growth of are pollen tubes were similarly impaired in both are and VF36 pistils. RNA-Seq was performed at optimal and stress temperatures in are, VF36, and the VF36 F3H overexpression line at multiple timepoints across pollen tube elongation. Differentially expressed gene numbers increased with duration of elevated temperature in all genotypes, with the largest number in are. These findings suggest potential agricultural interventions to combat the negative effects of heat-induced ROS in pollen that leads to reproductive failure. One sentence summaryFlavonol antioxidants reduce the negative impacts of elevated temperatures on pollen performance by reducing levels of heat induced reactive oxygen species and modulation of heat-induced changes in the pollen transcriptome.