Transgenic tomato plants with reduced expression of the sucrose transporter SlSUT2 showed higher efficiency of mycorrhization suggesting a sucrose retrieval function of SlSUT2 from the peri-arbuscular space back into the cell cytoplasm plant cytoplasm thereby limiting mycorrhiza fungal development. Sucrose uptake in colonized root cells requires efficient plasma membrane-targeting of SlSUT2 which is often retained intracellularly in vacuolar vesicles. Protein-protein interaction studies suggested a link between SISUT2 function and components of brassinosteroid biosynthesis and signaling. Indeed, the tomato DWARF mutant d(x) defective in BR synthesis (1) showed significantly reduced mycorrhization parameters. (2) The question has been raised whether the impact of brassinosteroids on mycorrhization is a general phenomenon. Here, we include a rice mutant defective in DIM1/DWARF1 involved in BR biosynthesis to investigate the effects on mycorrhization. A model is presented where brassinolides are able to impact mycorrhization by activating SUT2 internalization and inhibiting its role in sucrose retrieval.
Keywords: AM, arbuscular mycorrhiza; BR, brassinosteroids; DIM, diminuto; DRM, detergent resistant membrane; GO, gene ontology; LRR, leucine-rich repeat; MSBP, membrane steroid binding protein; Oryza sativa; PCR, polymerase chain reaction; RNA, ribonucleic acid; Rhizophagus irregularis; SNARE, soluble N-ethylmaleimide-sensitive-factor attachment receptor; SUC, sucrose carrier; SUT, sucrose transporter; arbuscular mycorrhiza; brassinosteroid; membrane trafficking; protein-protein interactions; sucrose transport.