Ectopic expression of specific GA2 oxidase mutants promotes yield and stress tolerance in rice.

Mikiko Kojima,Su‐May Yu,Hitoshi Sakakibara,Tuan‐Hua David Ho,Kun‐Ting Hsieh,Tzu‐Pi Huang,Miin‐Huey Lee,Liang‐Jwu Chen,Mirng‐Jier Jiang,Lin‐Chih Yu,Chi‐yu Chen,Yi‐Lun Liu,Ku‐Ting Chen,Shuen‐Fang Lo

doi:10.1111/pbi.12681

Abstract

SummaryA major challenge of modern agricultural biotechnology is the optimization of plant architecture for enhanced productivity, stress tolerance and water use efficiency (WUE). To optimize plant height and tillering that directly link to grain yield in cereals and are known to be tightly regulated by gibberellins (GAs), we attenuated the endogenous levels of GAs in rice via its degradation. GA 2‐oxidase (GA2ox) is a key enzyme that inactivates endogenous GAs and their precursors. We identified three conserved domains in a unique class of C20 GA2ox, GA2ox6, which is known to regulate the architecture and function of rice plants. We mutated nine specific amino acids in these conserved domains and observed a gradient of effects on plant height. Ectopic expression of some of these GA2ox6 mutants moderately lowered GA levels and reprogrammed transcriptional networks, leading to reduced plant height, more productive tillers, expanded root system, higher WUE and photosynthesis rate, and elevated abiotic and biotic stress tolerance in transgenic rice. Combinations of these beneficial traits conferred not only drought and disease tolerance but also increased grain yield by 10–30% in field trials. Our studies hold the promise of manipulating GA levels to substantially improve plant architecture, stress tolerance and grain yield in rice and possibly in other major crops.

Highlights

Rice is a major staple crop feeding more of the human population than any other crop, and increase in rice yield is crucial for meeting the world’s demand for food production in the several decades
We discovered that point mutation of certain amino acids of GA2ox6 conferred extraordinary beneficial traits such as semi-dwarfism, increase in grain yield and enhancement of abiotic and biotic stress tolerance in transgenic rice
Individual GA2ox6 mutants were expressed under the control of the Ubi promoter, and RT-PCR analyses showed that they were expressed at similar levels in independent transgenic rice lines (Figure S2)

Summary

Introduction

Rice is a major staple crop feeding more of the human population than any other crop, and increase in rice yield is crucial for meeting the world’s demand for food production in the several decades. The grain yield potential in rice is determined by both genetic and environmental factors Plant architectures such as height, tiller number and root system are important target traits for rice breeding. Slight reductions in GA levels result in semi-dwarfed plants that are more lodging-resistant in association with an improvement of harvest index (HI) (Khush, 1999) Manipulation of two such genes, Reduced height 1 (Rht1), encoding a wheat GA signalling factor, and semi-dwarf (sd1), encoding a rice GA biosynthesis enzyme, combined with N-fertilizer application, led to a quantum leap of yield in semi-dwarf cultivars of the respective plants. This provided the basis for the so-called Green Revolution between the 1960s and 1990s (Botwright et al, 2005; Peng et al, 1999)

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