Abstract
The low lysine content of waxy maize cannot meet the nutritional requirements of humans, livestock, or poultry. In the present study, the high-lysine genes o2 and o16 were backcrossed into wx lines using the maize high-lysine inbreds TAIXI19 (o2o2) and QCL3021 (o16o16) as donors and the waxy maize inbred line QCL5019 (wxwx) as a receptor. In the triple-cross F1, backcross, and inbred generations, the SSR markers phi027 and phi112 within the wx and o2 genes and the SSR marker umc1121 linked to the o16 gene were used for foreground selection. Background selection of the whole-genome SSR markers was performed for the selected individuals. The grain lysine content was determined using the dye-binding lysine method. The waxiness of the grain was determined with the I2-KI staining and dual-wavelength spectrophotometric analysis. The BC2F2 generation included 7 plants of genotype wxwxo2o2O16_, 19 plants of genotype wxwxo16o16O2_, and 3 plants of genotype wxwxo2o2o16o16. In these seeds, the average amylopectin content was 96.67%, 96.87%, and 96.62%, respectively, which is similar to that of QCL5019. The average lysine content was 0.555%, 0.380%, and 0.616%, respectively, representing increases of 75.1%, 19.9%, 94.3%, respectively, over QCL5019. The average genetic background recovery rate of the BC2F3 families was 95.3%, 94.3%, 94.2%, respectively. Among these 3 wxwxo2o2O16O16 families, 4 wxwxo2o2O16o16 families, and 3 wxwxo2o2o16o16 families, the longest imported parent donor fragment was 113.35 cM and the shortest fragment was 11.75 cM. No significant differences in lysine content were found between the BC2F4 seeds and the BC2F3 seeds in these 10 families. This allowed us to increase the lysine content of waxy corn and produce seeds with excellent nutritional characteristics suitable for human consumption, animal feed, and food processing. This may be of significance in the breeding of high-quality corn and in improvement of the nutrition of humans, livestock, and poultry.
Highlights
Waxy maize (Zea mays L. sinensis Kulesh), known as sticky maize, is one of nine sub-types of maize, first found in China and later found in other regions in Asia [1,2]
The main purpose of this study was to improve the nutritional quality of waxy corn by backcrossing the two high-lysine genes o2 and o16 into wx maize line using the multi-gene marker-assisted selection (MAS) combined with biochemical techniques, to produce waxy seeds with high lysine content, and to promote high-quality corn breeding and development of relevant industries
Two hundred and sixty-six SSR markers distributed on the 10 chromosomes of the maize genome were selected for the screening of polymorphisms between the three parents
Summary
Waxy maize (Zea mays L. sinensis Kulesh), known as sticky maize, is one of nine sub-types of maize, first found in China and later found in other regions in Asia [1,2]. The major mutations in waxy maize are insertion mutation, deletion mutation, and EMS mutagenesis [7,8,9,10] These mutations cause splicing errors and translation errors in pre-mRNA so that the Wx gene is not normally expressed. Starch in the grains of normal corn (WxWx) was found to be composed of amylose (25%) and amylopectin (75%). The GBSS-I activity of the wx mutant decreased by 5% to 95%, resulting in lower amylose content in grain and waxy corns with various levels of amylose. Sun and colleagues suggested that Wx was incompletely dominant to wx and that a dose effect was present between the amylopectin content and the endosperm wx gene [14]. Liu and Li indicated that it was difficult to achieve nearly 100% of amylopectin in waxy corn [15]
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