344 Li, Zhang, Wu, Guo, Liu, Wan, Jin, Hanh, Thoa, Chen, Liu, Chen, Liu, Wang, Zhai and Wan Fig. 5. Expression of two up-regulated genes during seed develop- ment of CSSL50-1 and seven sub-CSSLs. Total RNA was extracted from seeds at 6, 9, 12, 15 or 18 DAF. For each gene, the expression in Asominori seeds at 6, 9, 12, 15 or 18 DAF was set as a control. The relative expression value was obtained by the ratio of sub-CSSLs (or CSSL50-1) and Asominori. All data are means ± SD from three repli- cates. A: Os08g0534900, B: Os08g0536000 eating quality (Kobayashi et al. 2008, Takeuchi et al. 2007). In this study, based on RVA profile and analysis of sub- stituted segments in CSSLs, the effects of QTLs controlling RVA profile were detected in the same interval on chromo- some 8. The results confirmed the presence of QTLs control- ling eating quality on chromosome 8. The qAC-8 allele reported by Wan et al. (2004) was further dissected into two QTLs, qAC-8-1 and qAC-8-2, in this study. Moreover, qSBV-8, qCSV-8 and qAC-8-1 were partly overlapping, and different from the location of qAC-8-2. The candidate ge- nomic regions of the QTLs were narrowed down to four intervals: RM7580 to RM7356 (454 kb maximum), RM5351 to RM23200 (779 kb maximum), RM7356 to RM7556 (927 kb maximum), and RM23510 to RM23579 (776 kb maximum). Wan (2005a) identified two QTLs, qSBV-8 and qBDV-8, that were expressed stably across three or four environments on chromosome 8 using a recombinant inbred line (RIL) population derived from Asominori and IR24. Liu et al. (2011) also reported detection of chalkiness and starch properties QTLs at the same marker interval on chromosome 8 using CSSLs derived from IR24/Asominori. However, in this study, the QTL for SBV was expressed in only one environments and the QTL for BDV was not detected. In addition, qAC-8-2 was detected consistently across four environments and qCSV-8 across three, although the addi- tive effects of qCSV-8 and qAC-8-2 were not high. There may be several possibilities for the difference in results between the previous and present studies. One possibility was the existence of epistatic interactions between QTLs (Ebitani et al. 2005, Takeuchi et al. 2007). Interactions between loci can affect phenotypic difference between the tested QTL. Wan (2005a) reported that there was one locus on chromosome 2 having epistatic effect on the target inter- val of chromosome 8 for BDV in the RIL population. As sub-CSSLs are nearly isogenic to Asominori, the epistasis effect does not exist in sub-CSSLs. Another possibility was that genotype by environment (GE) interaction complicated the QTL mapping study (Takeuchi et al. 2007). Taken to- gether, the absent of epistatic QTL and the effects of envi- ronment may result in the identification of different QTLs in this study. Jiang et al. (2003) and Fujita et al. (1999) located the soluble starch synthase III (SSIII) and isoamylase (ISA) genes in the intervals V115–R1813 and C10122S–G1149 on rice chromosome 8, respectively. Since these two genes overlapped with the QTL cluster reported by Wan et al. (2004) in the interval G1149–R727 in high-density maps (Causse et al. 1994, McCouch et al. 2002), the QTL cluster for grain quality appeared to be associated with the starch synthesis pathway (Nakamura 2002, Smith et al. 1997). Al- though mapped to the same region, qAC-8-2 is not the ISA gene as revealed by detection of SSR markers. On the other hand, Aluko et al. (2004) found a QTL, amy-8, controlling AC, in the interval RM230–RM264 also on chromosome 8. Hao et al. (2009) mapped a QTL for AC, qAC-8, located in the interval RA2678–R1963, which also controlled chalki- ness (Fig. 2B). According to Fig. 2A, these three QTLs for AC overlap in the same region. In this study qAC-8-2 was narrowed down to a 776 kb of genomic region containing ten BAC (Fig. 3). It was reported that adverse environmental conditions readily affect the quality of rice grain. Drought stress, as well as sulphur deficiency which also activates antioxidation- related enzymes, can cause the increased activity of sucrose synthase, a key enzyme in starch biosynthesis, leading to the emergence of chalkiness (Lunde et al. 2008, Yang et al. 2001, 2002). The Os08g0534900 gene encodes a HEAT re- peat family protein concerned with adverse situations. In ad- dition, the Os08g0536000 gene encodes the beta subunit of pyruvate dehydrogenase E1 component involved in carbohy- drate metabolism. The two genes showed enhanced expres- sion in sub-CSSLs carrying the target qAC-8-2 allele, but not in sub-CSSLs lacking the target qAC-8-2 allele, implying their possible role in rice quality determination (Fig. 4). On the other hand, Guo et al. (2011) detected a QTL for PGWC using the same sub-CSSLs, designated as qPGWC-8, corre- sponding to the loci of qAC-8-1 and qCSV-8 identified here. Therefore, Os08g0534900 and Os08g0536000 genes might be involved in starch metabolism while not the formation of chalkiness. Thus, further genetic and molecular work is needed to