Asian cultivated rice Oryza sativa L. was domesticated from its wild ancestor, O. rufipogon. During domestication, the cultivated rice lost its seed-shattering behaviour. Previous studies have shown that two major quantitative trait loci (QTLs; qSH1 and sh4) are responsible for the seed-shattering degree. Here, we produced introgression lines carrying non-functional alleles from O. sativa ‘Nipponbare’ at the two major QTLs in the genetic background of wild rice O. rufipogon W630, and examined the effects of the two QTLs on seed shattering and abscission layer formation. The introgression lines, with Nipponbare alleles at either or both loci, showed complete or partial abscission layer formation, respectively, indicating that other unknown loci might be involved in enhancing seed shattering in wild rice. We detected a single QTL named qSH3 regulating seed-shattering degree using an F2 population between Nipponbare and the introgression line carrying Nipponbare alleles at the two QTLs. Although we generated an introgression line for qSH3 alone, no effects on seed shattering were observed. However, a significant effect on seed-shattering degree was observed for the introgression line carrying Nipponbare alleles at qSH3 and the two QTLs, suggesting an important role of qSH3 on seed shattering in coordination with the two QTLs.

Asian rice ( Oryza sativa L.) is consumed by more than half of the world's population. Despite its global importance, the process of early rice domestication remains unclear. During domestication, wild rice ( Oryza rufipogon Griff.) acquired non-seed-shattering behavior, allowing humans to increase grain yield. Previous studies argued that a reduction in seed shattering triggered by the sh4 mutation led to increased yield during rice domestication, but our experiments using wild introgression lines show that the domesticated sh4 allele alone is insufficient for shattering loss in O . rufipogon . The interruption of abscission layer formation requires both sh4 and qSH3 mutations, demonstrating that the selection of shattering loss in wild rice was not as simple as previously suggested. Here we identified a causal single-nucleotide polymorphism at qSH3 within the seed-shattering gene OsSh1 , which is conserved in indica and japonica subspecies but absent in the circum -aus group of rice. Through harvest experiments, we further demonstrated that seed shattering alone did not significantly impact yield; rather, yield increases were observed with closed panicle formation controlled by SPR3 and further augmented by nonshattering, conferred by integration of sh4 and qSH3 alleles. Complementary manipulation of panicle shape and seed shattering results in a mechanically stable panicle structure. We propose a stepwise route for the earliest phase of rice domestication, wherein selection of visible SPR3 -controlled closed panicle morphology was instrumental in the sequential recruitment of sh4 and qSH3 , which together led to the loss of shattering.

Loss of seed shattering was one of the key phenotypic changes selected for in the domestication of many crop species. Asian cultivated rice, Oryza sativa L., was domesticated from its wild ancestor, O. rufipogon, and three seed-shattering loci, qSH1, sh4 and qSH3, have been reported to be involved in the loss of seed shattering in cultivated rice. Here, we analysed the seed-shattering behaviour of wild rice using introgression lines carrying the cultivated alleles from O. sativa Nipponbare in the genetic background of wild rice, O. rufipogon W630. We first carried out fine mapping of the qSH3 region and found that the qSH3 locus is localized in an 850-kb region on chromosome 3. We then analysed the effects of the Nipponbare alleles at sh4 and qSH3 on seed-shattering behaviour in wild rice, as a mutation at qSH1 was not commonly found in rice cultivars. Seed-shattering behaviour did not change in the two types of introgression line independently carrying the Nipponbare-homozygous alleles at sh4 or qSH3 in the genetic background of wild rice. However, the introgression lines having the Nipponbare-homozygous alleles at both sh4 and qSH3 showed a reduction in the degree of seed shattering. Histological and scanning electron microscopy analyses revealed that abscission layer formation was inhibited around the vascular bundles in these lines. Since the qSH3 region, as well as sh4, has been shown to be under artificial selection, the interaction of mutations at these two loci may have played a role in the initial loss of seed shattering during rice domestication.

Short-term cultures of human lymphocytes were used to investigate the in vitro metabolism of benzene and its genotoxicity, and to monitor genetic health effects of lifestyles. Metabolic (S9) activation of benzene and its metabolites, catechol, hydroquinone, and phenol, caused an increase in sister-chromatid exchanges (SCEs) with different optimal concentrations of S9 mix for converting each compound into further reactive forms. The data indicate that catechol and hydroquinone can be optimally metabolized to produce reactive species, presumably benzo(semi)quinones, under conditions of lower metabolic activity than those necessary for phenol and benzene. We have further investigated the correlations between chromosome alterations (SCEs, structural aberrations and micronuclei) in peripheral lymphocytes and individual lifestyles. Healthy lifestyles, or "good health practices" examined were 1) not smoking, 2) not drinking too much alcohol, 3) doing physical exercise regularly, 4) sleeping more than 6 h per night, 5) keeping nutritional balance in meals, 6) not snacking, 7) having breakfast everyday, and 8) not having too much perceived stress. The persons were categorized into 3 groups having good, moderate and poor lifestyles by the number of good health practices they do. Mean frequencies of chromosome alterations in lymphocytes from men with poor lifestyles have been shown to be significantly higher than those in cells from men having good lifestyles.(ABSTRACT TRUNCATED AT 250 WORDS)

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