Targeted mutagenesis of the vacuolar H+ translocating pyrophosphatase gene reduces grain chalkiness in rice
Researchers at the University of Arkansas System Division of Agriculture (UADA) showed that by suppressing the activity of a grain-specific vacuolar H+ translocating pyrophosphatase (VPP5), chalk content of the grain could be reduced.
Grain chalk is an undesirable trait that impacts milling yield and cooking quality. Heat stress, specifically high nighttime temperature, is a major inducer of chalk, leading to yield losses and market value of rice. Based on the information that higher VPP5 activity leads to higher chalk content, Vibha Srivastava and her group at UADA used CRISPR-Cas9 to target promoter elements and suppress VPP5 activity during grain filling stages in rice. The resulting rice (vpp5 lines) showed 7 to 15-fold lower chalk content and improved grain weight. Most importantly, much lower chalk was induced by high nighttime temperature in vpp5 lines. Biochemical and gene expression analysis indicated improved starch biosynthesis and compact packing of starch granules as part of the mechanism.