Location: Crops Pathology and Genetics ResearchTitle: Identification of rice mutants with altered grain alkali digestion trait
|KIM, HYUNJUNG - University Of California, Davis|
|IMATONG, RALPH - University Of California, Davis|
Submitted to: Plant Breeding and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2020
Publication Date: 3/15/2020
Citation: Kim, H., Imatong, R.V., Tai, T. 2020. Identification of rice mutants with altered grain alkali digestion trait. Plant Breeding and Biotechnology. 8:19-27. https://doi.org/10.9787/PBB.2020.8.1.19.
Interpretive Summary: Eating and cooking quality (ECQ) is an important aspect of rice because almost the entire crop is use directly for human consumption in the form of whole milled grains or kernels. Gelatinization temperature (GT) is a major component of ECQ and reflects the time and energy required to cook rice as well as the texture of cooked and cooled cooked rice. Direct measurement of GT is laborious but an alternative method involving incubation of milled grains in dilute alkali solution is commonly used to estimate GT. This method is known as the alkali spreading (or digestion) value (ASV, ADV) assay and was employed in this study to screen a population of rice mutants derived from a low GT-type rice variety Kitaake. Two mutants with higher GT-type as measured by the ASV assay were identified (KDS-1623B and KDS-1824B) and genetic analysis revealed that both were due to recessive mutations. The KDS-1623B was determined to be the result of a mutation in the Isoamylase1 (ISA1) gene which is involved in biosynthesis of amylopection, one component of starch. Genetic resources for the identification of the KDS-1824B mutation have been developed but the mutation remains to be determined.
Technical Abstract: Gelatinization temperature (GT) is an important component of eating and cooking quality (ECQ) of rice. While direct measurement of GT is cumbersome, the alkali spreading value (ASV) test is a robust method commonly used to rapidly identify different GT-types. In this study, we employed a modified ASV assay to screen a population of chemically-induced rice (cv. Kitaake) mutants (n = 405). Two mutant families, KDS-1623B and KDS-1824B, with significantly lower ASV (higher GT-type) than wild type Kitaake (low GT-type) were isolated. A nonsynonymous homozygous mutation in the isoamylase-type starch debranching enzyme gene ISA1 was identified in KDS-1623B. The mutation (G2709T) is predicted to change a valine at position 354 to a leucine in the a-amylase catalytic domain of ISA1. This result is consistent with the shrunken endosperm exhibited by KDS-1623B grains and the replacement of starch with phytoglycogen in isa1 (sugary-1) mutants. The altered ASV trait in KDS-1824B appears to be controlled by a single recessive mutation, however the causal genetic lesion remains to be determined. These mutants will be useful resources for elucidating the complex nature of starch metabolism and its influence on ECQ of rice.