Analysis of Classic Tomato Mutants Reveals Influence of Leaf Vein Density on Fruit BRIX

Tomato bipinnate (bip) is a classic leaf mutant, with highly increased leaf complexity resulting from the loss of function of a BEL-LIKE HOMEODAMAIN (BELL) gene. Here, we analyzed several bip mutants and their isogenic wildtype backgrounds for a suite of leaf morphology traits, ranging from leaf complexity, leaflet shape and size, to leaf vascular density to investigate how changes in leaf morphology influence fruit traits. Our analyses showed an unexpected relationship between leaf vein density and fruit sugar levels, where leaf vein density was negatively correlated with fruit BRIX. RNA-Seq analysis suggested variation in Glucose-6-phosphate translocator2 (GPT2) gene expression caused correlated changes in leaf vein density and BRIX when bip mutant and wildtype were compared, suggesting that the correlation between leaf vein density and fruit sugar may result from the genes regulating leaf vein development that are also involved in regulating leaf sugar biosynthesis. Our results provide a resource for further exploration of the genetic basis for the complex relationship between fruit quality and leaf traits in natural populations.