Proc. Natl Acad. Sci. USA 112, 76–81 (2015)

Grain weight is an important component of crop yield. Although a few genes responsible for the grain weight of rice have been found, the precise regulatory mechanisms underlying this trait remain largely unknown. Now Xianjun Song, of Nagoya University, and colleagues have identified a histone acetyltransferase (OsglHAT1, a chromatin modifier) that controls the grain weight of rice.

The gene encoding OsglHAT1 was pinpointed to a 4-kb region of chromosome 6 by genetic mapping. Transgenic assays confirmed the positive regulatory effects of this gene on grain weight in both rice and Arabidopsis. A beneficial allele from the indica rice variety Kasalath, increased grain weight and biomass as a result of higher promoter activity and expression levels — compared with the more common allele from the japonica variety Nipponbare. OsglHAT1 increases cell numbers and consequent grain length, which facilitates grain filling.

That the underlying molecular mechanism stems from the transcription regulatory effect of OsglHAT1 was suggested by its histone acetyltransferase activity and nuclear localization. Indeed, OsglHAT1 transgenes modulate the expression of a large number of genes, consistently upregulating those involved in the cell cycle.

The beneficial Kasalath allele, present in only a few cultivated varieties, has not been actively explored by human selection. Therefore, its function as a chromatin modifier could be a promising new target for yield improvement in both rice and other crops.