图: phs8突变体穗发芽表型（左）及其ISA1影响穗发芽的调控机制（右）

Pre-harvest sprouting (PHS),physiologically mature grains germinating in spikes prior to harvest, is amajor natural problem in cereal crops such as rice, wheat, barley, and maize,which causes significant loss in grain yield, grain quality, and seedviability.

To illustrate the mechanism underlingthe rice PHS, scientists from CHU Chengcai’s group at the Institute of Geneticsand Developmental Biology, Chinese Academy of Sciences, has made a large scalescreening of phs mutants from their T-DNA mutant population. They reported thatthe mutations in the abscisic acid (ABA) biosynthetic genes could lead topre-harvest sprouting (phs1 to phs7).

Very recently, they characterizedthe phs8 mutant, which has a sugar-type endosperm. PHS8 encodes astarch-debranching enzyme, named isoamylase 1 (ISA1). Mutation of PHS8 causessugar accumulation in the endosperm, which in turn suppressed the expression oftwo major transcription factors in ABA signaling OsABI3 and OsABI5, resultingin pre-harvest sprouting in rice. In addition, overexpression of OsABI3 andABI5 could partially rescue the PHS phenotype of phs8.

 “PHS8/ISA1 is located in one QTL region whichcontrols seed dormancy and pre-harvest sprouting in rice, and populationgenetic analysis with 1529 rice varieties also showed that the PHS8/ISA1 sitewas strongly selected in Indica varieties, suggesting that PHS8/ISA1 could playan important role in the improvement of rice PHS tolerance” said Dr. XU Fan,one of team members of CHU’s group.

Source: Institute of Genetics andDevelopmental Biology

Time:2018.6.9