Rice is a staple food for nearly one-half of the world population. Although rice is grown in 112 countries, spanning an area from 53° latitude north to 35° south, about 90 percent of rice is grown and consumed in Asia. Rice provides fully 60 percent of the food intake in Southeast Asia and about 35 percent in East Asia and South Asia. Therefore, the continuing to develop new rice varieties is extremely important to guarantee Asia's food security and support the region's economic development.
In the past 10 years, we have made significant efforts to generate various biological resources for rice functional genomics. Besides tremendous efforts on germplasm collection, as a major effort, we have also generated approximately 25,000 independent T-DNA insertion lines in the rice japonica cv.
Nipponbare background. These lines have been used to screen for mutants involved in agronomically important traits related to the plant architecture, flowering time, and photosynthesis capacity, etc. The further characterization of representative mutants, will help us to understand the molecular basis for rice improvement.
The laboratory mainly focuses on the following aspects:
1. Molecular basis for crop yield improvement
Plant growth and development is dependent on the fixation of CO2
via photosynthesis. The photoassimilates fixed in the leaves (Source) has to be transported to other plant parts, e.g. roots and fruits (Sink). Interactions between source and sink are important for the regulation of plant growth and development, and also the crop yield. We are particularly interested in linking these physiological processes with genetic information by using rice as a model plant. To this end, large scale of screening of the mutants with altered source capacity (the rate of carbon export) and sink strength (seed size), was carried out. The genes responsible for the mutated phenotypes were isolated and characterized.
Figure 1. The mutants or germplasms with altered source capacity or sink strength. A, the germplasm with early senescence phenotype,
early senescence1 (es1); B, necrotic leaf sheath 1 (nls1) mutant with senescence initiated specifically from the leaf sheath; C, the germplasm with large seed size; D, the
photoassimilate deficiency1 (phd1) mutant phenotype.
2.Molecular basis for preharvest sprouting
The phenomenon of germination of cereal grains in the ear or panicle, usually under wet conditions shortly before harvest, is termed as preharvest sprouting or vivipary. PHS of cereal grains not only causes reduction of grain yield but also affects the grains quality. In contrast to the extensive molecular and genetic studies of seed dormancy in maize and
Arabidopsis, the molecular mechanism of seed dormancy in rice is poorly understood, mainly because of the lack of available mutants with reduced dormancy. Since PHS is a complex trait controlled by both environmental and genetic factors, we carried out a large-scale genetic screen for rice
preharvest sprouting (phs) mutants from T-DNA/Tos17 insertion mutant populations and obtained several hundred viviparous mutants. These mutants are valuable materials for elucidating the molecular mechanism of germination and dormancy in this model species. We wish that detail characterization of these mutants will be able to provide important clues on the molecular mechanism of preharvest sprouting in rice, which is not only a fundamental question in biology, but also a key for rice production. Moreover, these efforts should also have significant impacts on other crops such as wheat and barley that are susceptible to preharvest sprouting.
Figure 2. The preharvest sprouting
(phs) mutants. The mutant germinating in growth chamber with high humidity
(A), the mutant growing in the field of Hangzhou (South China) with high humidity
(B), and Beijing (North China) with low humidity (C).
3. Molecular breeding
Besides functional characterization of rice genes, we also made significant effort on the characterization of promoters with different specificities in rice. By using different approaches, we have obtained the promoters with different specificities, such as mesophyll cell specific, vascular tissue specific, anther and ovary specific, embryo specific promoters, etc. This work will facilitate the fine tuning of the agronomically important traits in the rice or other monocotyledonous crops by molecular design.
Overall, our final goal aims to use the knowledge, resources and tools obtained from our studies and combine approaches of genetics, molecular technologies, such as marker-assisted selection
and transgenic technology, in collaboration with breeders to develop superior hybrids and varieties that possess desirable characteristics such as higher yield potential, better disease resistance and drought tolerance. To achieve these goal, Jiaxin Hitech Breeding Centre, the first Hitech Breeding Centre with separate legal entity of the Chinese Academy of Sciences, was set up in Zhejiang Province, East China in 2005, and two super Japonica varieties, Xiushui 114 and Xiushui 134, have been developed in the Centre by marker-assisted selection, which now have widely planted in East China with total area of 4 million mu (300,000 hectares).