Abstract
Abscisic acid-, stress-, and ripening-induced (ASR) genes are involved in responding to abiotic stresses, but their precise roles in enhancing grain yield under stress conditions remain to be determined. We cloned a rice (Oryza sativa) ASR gene, OsASR1, and characterized its function in rice plants. OsASR1 expression was induced by abscisic acid (ABA), salt, and drought treatments. Transgenic rice plants overexpressing OsASR1 displayed improved water regulation under salt and drought stresses, which was associated with osmolyte accumulation, improved modulation of stomatal closure, and reduced transpiration rates. OsASR1-overexpressing plants were hypersensitive to exogenous ABA and accumulated higher endogenous ABA levels under salt and drought stresses, indicating that OsASR1 is a positive regulator of the ABA signaling pathway. The growth of OsASR1-overexpressing plants was superior to that of wild-type (WT) plants under paddy field conditions when irrigation was withheld, likely due to improved modulation of stomatal closure via modified ABA signaling. The transgenic plants had higher grain yields than WT plants for four consecutive generations. We conclude that OsASR1 has a crucial role in ABA-mediated regulation of stomatal closure to conserve water under salt- and drought-stress conditions, and OsASR1 overexpression can enhance salinity and drought tolerance, resulting in improved crop yields.
Highlights
The continuous use of irrigation systems and increasingly frequent dry periods lead to the simultaneous occurrence of salinity and drought on arable land around the world (Hu and Schmidhalter, 2005)
To investigate OsASR1 responses to abiotic stress, OsASR1 transcript levels were analyzed in leaf and root tissues before and after exposure to abscisic acid (ABA), NaCl, and drought (Figure 1B)
OsASR1 transcripts in leaves were most strongly expressed at 3 h after ABA treatment and at 6 h after NaCland drought-stress treatment, whereas OsASR1 was expressed continuously in root tissues under drought stress
Summary
The continuous use of irrigation systems and increasingly frequent dry periods lead to the simultaneous occurrence of salinity and drought on arable land around the world (Hu and Schmidhalter, 2005) Both salinity and drought are significant plant stressors with major impacts on plant development and grain yield, causing economic losses in agricultural production Plants have evolved numerous mechanisms to adapt to salinity and drought, such as stomatal adjustment, osmoregulation, selective uptake, and compartmentation of ions (Blumwald, 2000). These physiological responses are primarily regulated by the plant stress hormone abscisic acid (ABA) (Verma et al, 2016). ABA regulates guard cells to maintain their water content under osmotic stress and induces the expression of genes encoding proteins involved in cell dehydration resistance, including late embryogenesis abundant (LEA) proteins, water transporters, protein kinases, protein phosphatases, transcription factors, and enzymes involved in osmolyte synthesis (Fujita et al, 2011; Golldack et al, 2014)
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