Rice yield is determined by three key factors including tiller number, grain number per panicle and grain weight. Grain weight is largely affected by grain size. Although a number of grain size associated genes were identified in recent years, how these genes control grain size is largely unknown. In addition, in practical breeding processes, these three factors are usually found to be negatively associated each other, and it’s very hard to obtain a material with simultaneously improvement of the three aspects.

 

A team led by Prof. CHU Chengcai of the State Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology (IGDB), Chinese Academy of Sciences, recently cloned an important grain length associated locus named GL2, and further revealed the molecular mechanism of rice grain size control, by collaborating with Dr. ZHAO Mingfu from Fujian Academy of Agricultural Sciences for over ten years. They found GL2 can largely promote grain size, and also increase tiller number and grain number per panicle, introduction of GL2 into a rice cultivar named BBB leads to increase grain yield up to 16.6%.

 

GL2 encodes a member of growth regulatory factors named GRF4 and contains mutations in the target sequence of a class of micro-RNAs termed miR396. miR396 can target and inhibit GRF4 expression, but the mutations in GL2 will disrupt this kind of targeting and inhibition. Increased GRF4 will regulate the expression of a number of genes to activate the plant responses to a class of hormones termed brassinosteroids.

 

Brassinosteroids are well known for their multiple beneficial effects on plant growth and thus a great potential for crop improvement. “Plants carrying GL2 also have many beneficial agronomic traits including rapid germination, enhanced growth of source leaves, increased tiller number, a rapid grain filling rate, and significantly increased grain size and weight. Importantly, GL2 was not involved in regulating leaf angle, thus avoided the adverse trait of loose plant architecture that could be rendered by increased brassinosteroid response”, said by Dr. TONG Hongning, an Associate Professor in CHU’s lab, and also the co-first author of this paper.

 

“The most important value of GL2 is that it has moderately but specifically activated brassinosteroid responses”, Dr. CHE Ronghui, the first author of the paper added. “GL2 is a naturally existing gene resource, and could be directly utilized for rice breeding. At present, the scientists were still evaluating the gene effects in a number of different rice backgrounds”.

 

The work entitled “Control of grain size and rice yield by GL2-mediated brassinosteroid responses” was published on Nature Plants (doi:10.1038/nplants.2015.195) on December 21, and was supported by the grants from Natural Science Foundation and Chinese Academy of Sciences.

 

Contact:

Dr. CHU Chengcai

E-mail: ccchu@genetics.ac.cn