Mapping of a gene responsible for the difference in amylopectin structure between japonica-type and indica-type rice varieties

Abstract

The present investigation revealed that the alk and gel(t) genes, which cause the differences between a japonica rice variety Nipponbare and an indica rice variety Kasalath in terms of the disintegration of endosperm starch granules in alkali solution and their gelatinisation in a 4 M urea solution, respectively, cosegregated in backcross inbred lines derived from a cross between the two varieties. The segregation pattern of the profile for amylopectin chain-length, which was distinguished by enrichment in short chains of DP<==11 and depletion in intermediate-size chains of 12<==DP<==24 in japonica as compared with indica, was exactly the same as those of the above physico-chemical properties of starch granules, and the gene was designated as acl(t). Gene-mapping analysis showed that the starch synthase IIa ( SSIIa) gene is located at the alk locus on chromosome 6 in the rice genome. These results lead us to the possibility that different alleles of the SSIIa gene are responsible for differences in amylopectin structure between the two varieties, in that SSIIa plays a distinct role in the elongation of short chains within clusters (A+B(1) chains) of amylopectin. It is proposed that the activity of SSIIa in japonica rice is reduced in amount or functional capacity relative to the activity of this enzyme in indica rice. This, in turn, would explain why starch from japonica rice has a lower gelatinisation temperature than starch from indica rice and is more susceptible to disintegration in alkali or urea. The evidence for this hypothesis is that the alk(t), gel(t), acl(t) and SSIIa genes all map to the same locus.

Function and Characterization of Starch Synthase I Using Mutants in Rice

“…Chains with DP 6 to 7 and DP 16 to 19 increased while DP 8 to 12 chains decreased in all SSI mutant lines. These results sharply contrast with the findings in a SSIIa mutant (japonica rice) that DP # 10 chains decreased and DP 12 to 24 chains increased Umemoto et al, 2002), and in the maize SSIII mutant dull-1 where DP $ 37 chains decreased (Jane et al, 1999). Moreover, the magnitude of increase in DP 16 to 19 chains and decrease in DP 8 to 12 chains in all SSI mutant lines were closely related to the levels of the residual SSI activity (Figs.…”

“…On the other hand, the maximum change in amylopectin chain length in SSIIa mutant was 2.3% (D molar %) at DP 8 to 9 (Nakamura, 2002;Umemoto et al, 2002), which is larger than that for any SSI mutant. This suggests that the function of SSIIa might be hardly complemented by other SS isozymes including SSI.…”

“…Results of the comparison of the chain-length distribution of amylopectin between SSIIa mutants and their respective parents in rice (japonica rice; Nakamura et al, 2002;Umemoto et al, 2002), maize (sugary2; Zhang et al, 2004), barley (sex6; Morell et al, 2003), wheat (GSP-1 null; Yamamori et al, 2000), and antisense-SSII potato (Edwards et al, 1999) suggest that SSIIa preferentially elongates DP # 10 chains to DP 12 to 24 chains in vivo. Moreover, Nakamura et al (2005) showed that indica-type SSIIa expressed in E. coli elongates short DP 6 to 11 chains to DP 13 to 28 chains in japonica rice amylopectin in vitro.…”

“…In rice, there are 10 SS isoforms separated into five types; two granule-bound starch synthase (GBSS) isoforms (GBSSI and GBSSII) in the GBSS type, one SSI isoform in the SSI type, three SSII isoforms (SSIIa [SSII-3], SSIIb , and SSIIc ) in the SSII type, two SSIII isoforms (SSIIIa and SSIIIb ) in the SSIII type, and two SSIV isoforms (SSIVa and SSIVb ) in the SSIV type (Hirose and Terao, 2004). Mutants defective in GBSSI in several species (waxy rice [Sano, 1984]; waxy maize [Tsai, 1974]; waxy barley [Hordeum vulgare ;Eriksson, 1962]; waxy wheat [Triticum aestivum; Nakamura et al, 1995;Triticum monococcum;Fujita et al, 2001]; amf potato [Solanum tuberosum; Hovenkamp-Hermelink et al, 1987]; lam pea [Pisum sativum; Denyer et al, 1995]), SSIII of maize (dull-1; Gao et al, 1998), mutants deficient in SSIIa in rice (most japonica rice varieties are mutants of indica rice varieties [Umemoto et al, 2002;Nakamura et al, 2005]), in barley (sex6; Morell et al, 2003), in wheat (GSP-1 null; Yamamori et al, 2000) and in maize (sugary2; Zhang et al, 2004), and mutants for SSII in pea (rugosus5; Craig et al, 1998) have been identified and analyzed. Most recently, SSI (Delvalle et al, 2005) and SSIII (Zhang et al, 2005) mutants in Arabidopsis (Arabidopsis thaliana) leaves have been isolated.…”

The Effect of the Amount of Nitrogen Fertilizer on Starch Metabolism in Leaf Sheath of Japonica and Indica Rice Varieties during the Heading Period

“…The DBE activity of the second leaf sheath in Nipponbare was much lower than those observed in indica varieties. Recently, Umemoto et al (2002) proposed that the different alleles of starch synthase IIa gene may be responsible for the difference in the structure of amylopectin between a japonica and an indica varieties. It is possible that the difference in the DBE activity among these rice varieties affects the structure of amylopectin in the leaf sheath.…”