Abstract
Microsporogenesis in rice (Oryza sativa) plants is susceptible to moderate low temperature (LT; approximately 19°C) that disrupts pollen development and causes severe reductions in grain yields. Although considerable research has been invested in the study of cool-temperature injury, a full understanding of the molecular mechanism has not been achieved. Here, we show that endogenous levels of the bioactive gibberellins (GAs) GA4 and GA7, and expression levels of the GA biosynthesis genes GA20ox3 and GA3ox1, decrease in the developing anthers by exposure to LT. By contrast, the levels of precursor GA12 were higher in response to LT. In addition, the expression of the dehydration-responsive element-binding protein DREB2B and SLENDER RICE1 (SLR1)/DELLA was up-regulated in response to LT. Mutants involved in GA biosynthetic and response pathways were hypersensitive to LT stress, including the semidwarf mutants sd1 and d35, the gain-of-function mutant slr1-d, and gibberellin insensitive dwarf1. The reduction in the number of sporogenous cells and the abnormal enlargement of tapetal cells occurred most severely in the GA-insensitive mutant. Application of exogenous GA significantly reversed the male sterility caused by LT, and simultaneous application of exogenous GA with sucrose substantially improved the extent of normal pollen development. Modern rice varieties carrying the sd1 mutation are widely cultivated, and the sd1 mutation is considered one of the greatest achievements of the Green Revolution. The protective strategy achieved by our work may help sustain steady yields of rice under global climate change.
Highlights
Microsporogenesis in rice (Oryza sativa) plants is susceptible to moderate low temperature (LT; approximately 19°C) that disrupts pollen development and causes severe reductions in grain yields
The expression levels of both DREB2B and SLENDER RICE1 (SLR1)/DELLA strongly increased in response to LT treatment in developing anthers from the early premeiotic stage to the uninucleate pollen stage (Fig. 4). These results suggest the possibility that LT could disrupt GA-responsive pollen development through the transcriptional activation of SLR1/DELLA, which would be up-regulated by higher levels of DREB2B
The results clearly indicate that LT significantly reduced endogenous levels of bioactive GAs (GA4 and GA7) and Studies on cool-weather damage in rice have a long history, and have identified physiological responses including abnormal abortion of developing pollen followed by male sterility (Sakai, 1943; Nishiyama, 1976; 1982)
Summary
Microsporogenesis in rice (Oryza sativa) plants is susceptible to moderate low temperature (LT; approximately 19°C) that disrupts pollen development and causes severe reductions in grain yields. Grain yields in rice plants (Oryza sativa) are often reduced by exposure to moderate low temperature (LT), which is termed cool-temperature damage. It is estimated that the net effect of cool-temperature damage is an annual loss of at least three to five million tons of rice in East Asia (Li and Guo, 1993). Unexpected climate change, such as abnormally hot or cool summer temperatures, has occurred repeatedly during recent years due to the El Niño/La Niña-Southern Oscillation (Intergovernmental Panel on Climate Change, 2007). The sd mutant is considered one of the greatest achievements of the Green
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