SlTLFP8reduces water loss to improve water-use efficiency by modulating cell size and stomatal density via endoreduplication

Improving plant water-use efficiency (WUE) is important to plant survival and crop yield in the context of water limitation. In this study,SlTLFP8(Tubby-like F-box protein 8) was identified as an osmotic-induced gene in tomato. Transgenic tomato with up-regulated expression ofSlTLFP8showed enhanced water-deficient resistance, whereas knockout mutants generated by CRISPR/Cas9 were more sensitive to water deficit.SlTLFP8overexpression significantly enhanced WUE by suppressing transpiration under both water-sufficient and water-deficient conditions. Further study showed that overexpressingSlTLFP8significantly increased leaf epidermal cell size and thereby decreased stomatal density 10-20%, converselySlTLFP8knockout resulted in decreased cell size and thereby increased stomatal density 20-50%.SlTLFP8overexpression and knockout modulated ploidy levels in leaf cells. Changes in expression of cell cycle related genes also indicated thatSlTLFP8affected cell size and stomatal density through endocycle transition. Despite changes in stomata density and transpiration, altering the expression ofSlTLFP8did not change photosynthesis. Additionally, biomass was not altered and there was little difference in fruit yield for transgenic and wild type lines under water-sufficient and water-deficient conditions. Our results demonstrate the effect ofSlTLFP8on endoreduplication and the potential ofSlTLFP8for improvement of WUE.