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

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 welldeveloped 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 F 1 plants and segregation data in F 2 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 qSD s -7-1 for seed dormancy, implying that this region might represent a domestication block in the evolutionary pathway of rice.

Threshing force of paddy as affected by loading manner and grain position on the panicle

“…Varieties with moderate shattering are favored where rice is harvested by large combine harvester-threshers, while harvesting using a small head-feeding combine is the most efficient when hard-shattering to non-shattering varieties are used (Kobayashi 1990). Easy shattering varieties are not acceptable to any of the farmers because they cause severe yield loss no matter what type of harvesting is practiced (Ji et al 2006).…”

Genetic analysis of seed-shattering genes in rice using an F3:4 population derived from an Oryza sativa x Oryza rufipogon cross

“…QTL analysis was also performed for other known shattering loci of qSH4 and sh-h (Ji et al, 2006) to compare the effect of the QTL on qSH-1 shattering in our population. Eight SSR markers around the qSH-4 locus on chromosome 4 were analyzed (Table 1 and Figure 5b).…”

“…The physical location of qSH-4 was placed between RM3648 and RM1113, for which the LOD score was 4. The seedshattering locus sh-h was present on chromosome 7 and linked very closely with the Rc locus, which determined the pericarp color in rice (Ji et al, 2006;Sweeney et al, 2006) (Figure 5c). We previously designed 5 sets of allele-specific primers using the in/del information (Table 1) (Sweeney et al, 2006).…”

“…Four independent groups reported genes or gene blocks involved in seedshattering in rice (Konishi et al, 2006;Sweeney et al, 2006;Ji et al, 2006). Using a genomic approach and association analysis, Konishi et al (2006) demonstrated a single nucleotide change T→G in a qSH-1 locus at a QTL on chromosome 1 that caused seedshattering and accounted for 68.8% of the total phenotypic variations in a segregating population between japonica cultivars Nipponbare/Kasalath.…”

“…nivara, showed that 7 single-nucleotide mutations at the LOC_Os04g57530 locus (TIGRE rice annotation number) were involved in seed shattering in wild Oryza species (O. nivara, O. rufipogon, O. glumaepatulae, O. barthii, O. longistaminata, and O. meridionalis). Using the easy-shattering mutant of japonica-type rice, Ji et al (2006) localized the shattering gene, shh, to chromosome 7. The sh-h locus is closely associated with the anthocyanin synthase gene Rc (Sweeney et al, 2006).…”