Abstract
SummaryAlthough a variety of transgenic plants that are tolerant to drought stress have been generated, many of these plants show growth retardation. To improve drought tolerance and plant growth, we applied a gene‐stacking approach using two transcription factor genes: DEHYDRATION‐RESPONSIVE ELEMENT‐BINDING 1A (DREB1A) and rice PHYTOCHROME‐INTERACTING FACTOR‐LIKE 1 (OsPIL1). The overexpression of DREB1A has been reported to improve drought stress tolerance in various crops, although it also causes a severe dwarf phenotype. OsPIL1 is a rice homologue of Arabidopsis PHYTOCHROME‐INTERACTING FACTOR 4 (PIF4), and it enhances cell elongation by activating cell wall‐related gene expression. We found that the OsPIL1 protein was more stable than PIF4 under light conditions in Arabidopsis protoplasts. Transactivation analyses revealed that DREB1A and OsPIL1 did not negatively affect each other's transcriptional activities. The transgenic plants overexpressing both OsPIL1 and DREB1A showed the improved drought stress tolerance similar to that of DREB1A overexpressors. Furthermore, double overexpressors showed the enhanced hypocotyl elongation and floral induction compared with the DREB1A overexpressors. Metabolome analyses indicated that compatible solutes, such as sugars and amino acids, accumulated in the double overexpressors, which was similar to the observations of the DREB1A overexpressors. Transcriptome analyses showed an increased expression of abiotic stress‐inducible DREB1A downstream genes and cell elongation‐related OsPIL1 downstream genes in the double overexpressors, which suggests that these two transcription factors function independently in the transgenic plants despite the trade‐offs required to balance plant growth and stress tolerance. Our study provides a basis for plant genetic engineering designed to overcome growth retardation in drought‐tolerant transgenic plants.
Highlights
Drought is one of the most serious environmental stresses that affect global agriculture
We propose that OsPIL1 partially enhances plant growth and accelerates flowering time, even in the double overexpressors, without negative effects on DEHYDRATIONRESPONSIVE ELEMENT-BINDING 1A (DREB1A)-mediated drought stress tolerance
In the absence of MG132, the PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) protein was degraded in a light- and time-dependent manner as previously reported (Nozue et al, 2007), whereas the OsPIL1 protein was more stable under the same conditions (Figure S1b)
Summary
Drought is one of the most serious environmental stresses that affect global agriculture. To ensure a stable supply of foods and biomass materials, it is imperative to improve drought stress tolerance in crops. A variety of transgenic plants that are tolerant to drought stress have been generated, many of these plants show growth retardation (Yamaguchi-Shinozaki and Shinozaki, 2006). To reduce the negative effects on plant growth, stress-inducible promoters have been used to drive the expression of transgenes in transgenic plants (Bhatnagar-Mathur et al, 2007; Kasuga et al, 1999; Pino et al, 2007; Suo et al, 2012). Growth retardation appears to be unavoidable under the long-term drought stress conditions because of the prolonged overexpression of transgenes, even when using stress-inducible promoters. Additional approaches are required to improve the growth of stress-tolerant plants
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