Brassinosteroids and sucrose transport in mycorrhizal tomato plants.

Silencing of SlSUT2 expression in tomato plants leads to a dwarfed phenotype, reduced pollen vitality and reduces pollen germination rate. Male sterility of flowers, together with a dwarfed growth behavior is reminiscent to brassinosteroid defective mutant plants. Therefore we aimed to rescue the SlSUT2 silencing phenotype by local brassinosteroid application. The phenotypical effects of SlSUT2 down-regulation could partially be rescued by epi-brassinolide treatment suggesting that SlSUT2 interconnects sucrose partitioning with brassinosteroid signaling. We previously showed that SlSUT2 silenced plants show increased mycorrhization and, this effect was explained by a putative sucrose retrieval function of SlSUT2 at the periarbuscular membrane. More recently, we reported that the symbiotic interaction between Solanaceous hosts and AM fungi is directly affected by watering the roots with epi-brassinolide. Here we show that the SlSUT2 effects on mycorrhiza are not only based on the putative sucrose retrieval function of SlSUT2 at the periarbuscular membrane. Our analyses argue that brassinosteroids as well as SlSUT2 per se can impact the arbuscular morphology/architecture and thereby affect the efficiency of nutrient exchange between both symbionts and the mycorrhizal growth benefit for the plant.