Pre-harvest sprouting (PHS), physiologically mature grains germinating in spikes prior to harvest, is a major natural problem in cereal crops such as rice, wheat, barley, and maize, which causes significant loss in grain yield, grain quality, and seed viability.
To illustrate the mechanism underling the rice PHS, scientists from CHU Chengcai's group at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, has made a large scale screening of phs mutants from their T-DNA mutant population.
They reported that the mutations in the abscisic acid (ABA) biosynthetic genes could lead to pre-harvest sprouting (phs1 to phs7).
Very recently, they characterized the phs8 mutant, which has a sugar-type endosperm. PHS8 encodes a starch-debranching enzyme, named isoamylase 1 (ISA1). Mutation of PHS8 causes sugar accumulation in the endosperm, which in turn suppressed the expression of two major transcription factors in ABA signaling OsABI3 and OsABI5, resulting in pre-harvest sprouting in rice.
In addition, overexpression of OsABI3 and ABI5 could partially rescue the PHS phenotype of phs8.
"PHS8/ISA1 is located in one QTL region which controls seed dormancy and pre-harvest sprouting in rice, and population genetic analysis with 1529 rice varieties also showed that the PHS8/ISA1 site was strongly selected in indica varieties, suggesting that PHS8/ISA1 could play an important role in the improvement of rice PHS tolerance" said Dr. XU Fan, one of team members of CHU's group.
This work was supported by the grant from the Chinese Academy of Sciences.
Left, pre-harvest sprouting phenotype of phs8. Right, the molecular mechanism of ISA1 influence on pre-harvest sprouting. (Image by IGDB)
