The α-subunit of the rice heterotrimeric G protein, RGA1, regulates drought tolerance during the vegetative phase in the dwarf rice mutant d1.

Ángel Ferrero-Serrano,Sarah M Assmann

doi:10.1093/jxb/erw183

Ángel Ferrero-Serrano, Sarah M Assmann

Open Access

https://doi.org/10.1093/jxb/erw183

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Abstract

Essential in the Green Revolution was the development of high-yielding dwarf varieties of rice (Oryza sativa L.), but their selection was not based on responses to water limitation. We studied physiological responses to progressive drought of the dwarf rice mutant, d1, in which the RGA1 gene, which encodes the GTP-binding α-subunit of the heterotrimeric G protein, is non-functional. Wild-type (WT) plants cease net carbon fixation 11 days after water is withheld, while d1 plants maintain net photosynthesis for an additional week. During drought, d1 plants exhibit greater stomatal conductance than the WT, but both genotypes exhibit the same transpirational water loss per unit leaf area. This is explained by a smaller driving force for water loss in d1 owing to its lower leaf temperatures, consistent with its more erect architecture. As drought becomes more severe, WT plants show an accelerated decline in photosynthesis, which may be exacerbated by the higher leaf temperatures in the WT. We thus show how a rice mutant with dwarf and erect leaves has a decreased susceptibility to water stress. Accordingly, it may be useful to incorporate RGA1 mutation in breeding or biotechnological strategies for development of drought-resistant rice.

Highlights

Rice (Oryza sativa L.) is the staple food for more than half of the world’s population and is one of the three major cereal crops
This can be attributed to our deliberate choice of a large ratio of soil volume to biomass in these studies: the absence of any statistical difference between the curves in Fig. 1A demonstrates that transpirational withdrawal of water from the soil by the small plants of both genotypes is minor compared with soil evaporative water loss
It is interesting to note that, regardless of whether the photosynthetic rate is plotted relative to time after drought initiation (Fig. 1C) or relative to relative soil water content (RSWC) (Fig. 1D), there was an increase in photosynthesis in d1 as soil dried from saturating conditions to ~50% RSWC, which occurs at 4 d after initiation of drought

Summary

Introduction

Rice (Oryza sativa L.) is the staple food for more than half of the world’s population and is one of the three major cereal crops. Dwarf rice varieties with reduced stature and other associated traits such as erect leaves were a cornerstone of Green Revolution breeding programs (Duvick and Cassman, 1999; Khush, 2001). These dwarf varieties provide the advantages of an increased harvest index and decreased lodging (Hedden 2003). D1 was among the first rice mutants to be identified by segregation analysis (Akemine, 1925) It was originally found in Hokkaido in 1912 as a natural mutant originating from the Akage cultivar (Nagai, 1959), an inbred line developed from a 3434 | Ferrero-Serrano and Assmann landrace in order to increase grain size (Shomura et al, 2008). Rice RGA1 encodes a 380 amino acid protein and, in this study, we investigated the d1-1 mutant in cultivar Taichung 65 (T65) in which there is a 2 bp deletion in RGA1 that results in a protein null phenotype based on immunoblot analysis (Oki et al, 2009b)

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