Quantitative trait loci affecting amlose, amylopectin and starch content in maize recombinant inbred lines

The loci explaining the variability of quantitative traits related to starc h content and composition (amylose, amylopectin and water soluble fraction) were searched for in maize kernels. Multifactorial genetic methods were us ed to detect and locate QTLs (quantitative trait loci) on a genetic map con sisting mainly of RFLP markers for genes with known function. The genetic m aterial was recombinant inbred lines originating from parents differing in starch structure (dent vs. flint). Kernels were harvested from field grown plants for two successive years and under two pollination systems. Main eff ect and epistasis QTLs were detected using two methods, composite interval mapping (MQTL) and ANOVA. Despite large year-to-year differences, physiolog ically meaningful co-locations were observed between trait QTLs. Moreover, the number of expressed sequences on our map allowed the search for co-loca tions between QTLs and genes involved in carbohydrate metabolism. The main co-location was between an amylose QTL and Shrunken 2 (SH2) locus, on chrom osome 3 (SH2 encoding for the large subunit of ADPglucose pyrophosphorylase ). The importance of this locus as a candidate gene for a starch QTL is in agreement with previous studies based either on QTL co-locations or on reve rtant analysis. Other co-locations were observed between amylose and amylop ectin QTLs and the two loci of IVR1 invertase genes on chromosomes 2 and 10 . Further comparison with previously detected QTLs for carbohydrate metabol ism in maize leaves showed consistent co-location in map regions devoid of candidate genes, such as near chromosome 1S telomere. The possible contribu tion of regulatory genes in this region is discussed. (C) 2000 Editions sci entifiques et medicales Elsevier SAS.