Characterization and Mapping of a Shattering Mutant in Rice That Corresponds to a Block of Domestication Genes

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Abstract
Easy shattering reduces yield due to grain loss during harvest in cereals. Shattering is also a hindrance in breeding programs that use wild accessions because the shattering habit is often linked to desirable traits. We characterized a shattering mutant line of rice, Hsh, which was derived from a nonshattering japonica variety, Hwacheong, by N-methyl-N-nitrosourea (MNU) treatment. The breaking tensile strength (BTS) of the grain pedicel was measured using a digital force gauge to evaluate the degree of shattering of rice varieties at 5, 10, 15, 20, 25, 30, 35, and 40 days after heading (DAH). The BTS of Hwacheong did not decrease with increasing DAH, maintaining a level of 180–240 gf, while that of Hsh decreased greatly during 10–20 DAH and finally stabilized at 50 gf. Optical microscopy revealed that Hsh had a well-developed abscission layer similar to the wild rice Oryza nivara (accession IRGC105706), while Hwacheong did not produce an abscission layer, indicating that the shattering of Hsh was caused by differentiation of the abscission layer. On the basis of the BTS value and morphology of the abscission layer of F1 plants and segregation data in F2 populations, it was concluded that the easy shattering of Hsh was controlled by the single recessive gene sh-h. The gene sh-h was determined to be located on rice chromosome 7 by bulked segregant analysis. Using 14 SSR markers on rice chromosome 7, the gene sh-h was mapped between the flanking markers RM8262 and RM7161 at distances of 1.6 and 2.0 cM, respectively. An SSR marker Rc17 cosegregated with the gene sh-h. The locus sh-h for shattering was tightly linked to the Rc locus conferring red pericarp, as well as a QTL qSDs-7-1 for seed dormancy, implying that this region might represent a domestication block in the evolutionary pathway of rice.