No abstract

In this paper, we characterized the Wx-mq gene for low amylose content in a rice variety, Milky Queen, at the molecular level. The Wx-mq gene was cloned by RT-PCR, and a nearly full-length cDNA sequence of the gene was determined. Sequence comparison between the Wx-mq gene and the wild type allele (Wx-b), cloned from cv. Koshihikari, revealed that two base changes existed within the coding region; a G to A base change at nucleotide position 497 and a T to C base change at nucleotide position 595. Each nucleotide substitution should generate a missense base change (an Arg-158 to His-158 change in exon4, and a Tyr-191 to His-191 change in exon5). However, it is not known which missense mutation is essential for the activity of the WX protein. To identify rice varieties and lines, which harbored the Wx-mq gene, PCR primers were designed at the gene level. These primers were able to amplify the Wx-mq specific 741 bp band in Milky Queen, and in other rice variety and lines, Milky Princess, Joiku 436 and Etsunan 190, all of which have the same pedigree as that of Milky Queen. On the other hand, no 741 bp band was amplified with the primers in Koshihikari which harbored the wild type allele (Wx-b), and the other low-amylose content variety and line, Snow Pearl and NM391, which do not have the pedigree. Thus, it is possible to detect the Wx-mq gene by PCR.

Stable carbon isotope ratio (δ13C) in plants has been suggested as a useful indicator for cumulative Ci/Ca signature in a leaf, water use efficiency, and crop productivity, and is known to have genotypic variation in rice (Oryza sativa L.). We conducted a field study to identify quantitative trait loci (QTLs) for δ13C and other related leaf traits, such as leaf N, specific leaf area, and SPAD value, using recombinant inbred lines derived from an indica × japonica cross grown under flooded conditions. We also examined the genetic associations of δ13C with yield, yield components, and biomass productivity. Putative QTLs for δ13C were identified on chromosomes 2, 4, 8, 9, 11, and 12 across plant parts, stages, and years. Differential expression of QTL for δ13C among stages suggests that each QTL had different functions by stages. The QTLs for δ13C were associated with a few colocated QTLs for leaf traits indicating that their physiological and genetic associations with leaf traits may be complex. Values of δ13C at maturity were negatively correlated with harvest index and grain yield. However, genetic association of these traits could not be clarified due to the absence of co‐located QTLs. Further examination would be useful to elucidate the physiological and morphological functions of QTLs for δ13C found in this study.

To identify the chromosomal regions controlling the eating quality of cooked rice, we performed a quantitative trait locus (QTL) analysis using 93 backcross inbred lines (BILs) and 39 chromosome segment substitution lines (CSSLs) derived from crosses between a japonica rice cultivar Koshihikari (glossier appearance, tasty, sticky and soft eating quality of rice when cooked) and an indica cultivar Kasalath (less glossy appearance, less sticky and hard eating quality of rice when cooked). We evaluated the eating quality of rice including overall evaluation (OE), glossiness (GL), taste (TA), stickiness (ST) and hardness (HA) in each line based on the sensory test of cooked rice. Twenty-one QTLs for eating quality were mapped to eight regions on chromosomes 1, 2, 3 (two regions), 6, 7, 9 and 10. The Koshihikari alleles at 19 out of 21 QTLs increased the eating quality, while the Kasalath alleles at the other two QTLs increased the eating quality. We also mapped the QTLs for chemical properties, such as amylose content (AC) and protein content (PC), which affected the eating quality. Four QTLs in the terminal region of the short arm of chromosome 3 and five QTLs on chromosome 6 for eating quality were mapped to the same region as that of the QTLs for AC. Three QTLs on chromosome 1 for eating quality were also mapped to the same region as that of a QTL for PC. The chromosome positions of the other QTLs for eating quality did not coincide with those of the QTLs for AC and PC. Six out of 21 QTLs for eating quality, qTA3, qOE6, qGL6, qTA6, qST6 and qHA6, were commonly identified by analysis using both BILs and CSSLs. One QTL, qTA3, was not a locus of AC, PC or known eating genes. Thus the QTL was mapped in the interval between the SSR markers RM1332 and RM6676 in the middle region of the short arm of chromosome 3 by fine mapping of three sub-CSSLs. Five QTLs, qOE6, qGL6, qTA6, qST6 and qHA6, seemed to be associated with the Waxy (Wx) gene located on chromosome 6.