Novel mutant "low grain weight" found affecting grain size

A rice (Oryza sativa) mutant, low grain weight (lgw) was isolated by a research team led by Prof. Wu Yuejin from Hefei Institutes of Physical Science (HFIPS) of Chinese Academy of Sciences (CAS). In this research, they proved that lgw mutation led to reduced grain length through decreasing cell elongation and proliferation.

The result was published in Frontiers in Plant Science.

Grain weight is a major determinant in rice yield, which is tightly associated with grain size. However, despite decades of studies, the underlying molecular mechanisms for regulating grain size still remained unclear.

In this research, the research team obtained rice small grain mutant lgw by ion beam mutagenesis. They found that lgw was a new allelic variation of brittle culm gene BC12 by map-base cloning approach.

The lgw mutation site was located in the nuclear localization signal region of BC12, which affected its nuclear localization. Overexpression of this gene could significantly increase grain length and Thousand Grain Weight.

"We can tell that LGW is a positive regulator for regulating grain length," said YE Yafeng, first author of the paper.

LGW/BC12 affected grain size by directly binding to the promoter of the grain length gene GW7 and regulating its transcription.

BC12 was a typical brittle culm gene, and its mutation would lead to brittle culm phenotype, but the straw brittleness of lgw mutant was not obvious. It was speculated that LGW/BC12 depended on its different biological functions in regulating cell wall synthesis and grain size.

"These findings revealed that LGW played an important role in regulating grain size, and manipulation of this gene provided a new strategy for regulating grain weight in rice." Said YE.