Brassinosteroids mediate the effect of soil-drying during meiosis on spikelet degeneration in rice

This study investigated whether and how brassinosteroids (BRs) mediate the effect of soil-drying during meiosis on spikelet degeneration in rice (Oryza sativa L.). A field-grown rice cultivar was exposed to three soil moisture treatments during meiosis: well-watered (WW), moderate soil-drying (MD) and severe soil-drying (SD). Compared with the WW treatment, the MD treatment enhanced BRs biosynthesis, reduced spikelet degeneration, and increased grain yield. The SD treatment had the opposite effects. Changes in the levels of adenosine triphosphate (ATP), energy charge, activities of enzymes involved in energy metabolism, including cytochrome C oxidase (CCO) and succinate dehydrogenase (SDH), and total antioxidant capacity (T-AOC) were consistent with those in BRs levels, whereas the hydrogen peroxide (H2O2) content, vacuolar processing enzyme genes (OsVPE2 and OsVPE3) expression levels and the degree of nuclear DNA fragmentation showed the opposite trend. Knockdown of the BRs synthesis gene OsD11 or application of a BRs biosynthesis inhibitor to young panicles vastly decreased the BRs and ATP contents, energy charge, CCO and SDH activities, and T-AOC in young panicles but increased the H2O2 content, OsVPE2 and OsVPE3 expression, and spikelet degeneration compared to the control, and the opposite effects were observed when exogenous BRs were applied. Therefore, BRs likely mediate the effect of soil-drying on spikelet degeneration, and elevated BRs levels in rice panicles inhibit spikelet degeneration under moderate soil-drying during meiosis by elevating antioxidant capacity and energy status.