Salt stress-induced remodeling of sugar transport: a role for promoter alleles of SWEET13

Sucrose, the primary carbon form synthesized by photosynthesis, is transported via the phloem for proper plant development and productivity. However, long-distance sucrose transport can become unbalanced under adverse environmental conditions. Therefore, we highlight the influence of salt stress on sugar partitioning in source versus sink tissues in sorghum under generative development including the role of stress induced sucrose transporter expression. The two sorghum genotypes displayed different responses to salinity in terms of resource allocation, in Della sugar was translocated to the stem and roots, whereas in Razinieh sugars were directed towards the grains. In Della, the unloading of sucrose in the roots was associated with increased expression levels of SbSUT6 and SbSWEET6, while in the internodes, sucrose unloading correlated with elevated levels of SbSWEET13 and the ABA-dependent transcription factor SbbZIP-TF-TRAB1. Conversely, in Razinieh, the expression of SbSUT2 in the flag internodes was linked to enhanced panicle development. In addition, a differential activation of SbSWEET13 and SbSUT6 promoters by ABA and MeJA was elucidated using dual-luciferase reporter assay in sorghum protoplasts. Finally, we arrive at a model where dynamic remodeling of sugar transport during generative development is crucial for the response to salt stress, and more manifested in sink tissues.