Brassinosteroids promote starch synthesis and the implication in low-light stress tolerance in Solanum lycopersicum

Starch, as the stored form of carbohydrates in plants, can be degraded into soluble sugars to meet the needs of metabolism when photosynthesis is closed. However, the role of starch synthesis in response to prolonged low light stress in greenhouse crops is unclear. In this study, we found that overexpression of brassinosteroids (BRs) synthesis gene DWARF (DWF) increased accumulation of starch and soluble sugars in tomato leaves, whereas BRs deficient mutant dwf exhibited the opposite changes. The expressions of genes encoding the starch synthesis enzymes such as granule bound starch synthase (GBSS) and ADP-glucose pyrophosphorylase (AGPase) were significantly enhanced by overexpression of DWF, but decreased in dwf mutant. The enzyme activities of GBSS and AGPase were regulated by BRs in a similar way. Exogenous 24-epibrassinolide (EBR) also increased starch synthesis and promoted plant growth. Furthermore, increasing BRs synthesis or exogenous EBR delayed senes-cence and enhanced plant performance under prolonged low light stress. Our results demonstrated that BRs-induced low light stress was closely associated with starch synthesis. The study deepened our understanding on the roles of BR in carbohydrate metabolism, and implicated the application of BRs in coping with the low light stress in a context of global climate changes.