Kernel lysine content does not increase in some maize opaque2 mutants

Maize Center, Department of Crop Genetics and Breeding, Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100081, People's Republic of China.
Planta (Impact Factor: 3.26). 08/2011; 235(1):205-15. DOI: 10.1007/s00425-011-1491-z
Source: PubMed


The recessive mutant allele of the opaque2 gene (o2) alters the endosperm protein pattern and increases the kernel lysine content of maize (Zea mays L.). In this study, sequencing results showed that the o2 mutant was successfully introgressed into 12 elite normal maize inbred lines by marker assisted selection (MAS). The average genetic similarity between these normal inbred lines and their o2 near-isogenic lines (NILs) was more than 95%. Kernel lysine content increased significantly in most of o2 NILs lines relative to normal elite inbreds, but remained unchanged in the genetic backgrounds Dan598o2 and Liao2345o2. Moreover, the kernel characteristics of these two o2 NILs did not differ from the other inbred lines. The results of lysine content analysis in the F1 hybrids between Liao2345o2 and Dan598o2 and other o2 NILs demonstrated that gene(s) other than opaque2 may control kernel lysine content in these two o2 NILs. The results of zein analysis showed that 22-kD α-zein synthesis was reduced or absent, and the 19-kD α-zein synthesis was greatly reduced compared with the recurrent parents in most o2 NILs except for Dan598o2 and Liao2345o2. Our results indicate that gene(s) other than opaque2 may play more important roles in zein synthesis and kernel lysine content in some maize genetic backgrounds.

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    • " et al . ( 2005 ) and Gupta et al . ( 2013 ) introgressed o2 into elite maize inbreds using marker - assisted backcross breeding strategy . The improved inbreds ( with 25% opaqueness ) though possessed significantly higher tryptophan than the original inbred , and the tryptophan concentration was not as high as respective donor parents . Further , Zhao et al . ( 2012 ) improved several inbreds by introgressing o2 allele . In two of the introgressed o2 - inbreds , lysine did not show any increase as com - pared to original inbreds . In all these cases , important amino acids modifier loci were lost in the backcross generations before o2 could attain homozygosity . Selection of these modifier loci dur"
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    ABSTRACT: Modifier loci in QPM play a vital role in achieving acceptable degree of kernel hardness and accumulation of lysine and tryptophan. This study was undertaken to characterize a set of diverse QPM inbreds using SSRs linked to endosperm and amino acids modifier loci for their effective utilization in the breeding programme. Significant variation was observed for endosperm modification (25-100% opaqueness), tryptophan (0.056-0.111%) and lysine (0.223-0.444%). Generally, inbreds with soft endosperm possessed more tryptophan and lysine than inbreds with higher vitreousness. SSRs generated 341 alleles with two to seven alleles per locus. The frequency of unique and rare alleles was more for amino acid modifications, compared to endosperm modifications. Phylogenetic analyses grouped the inbreds into three major clusters, and the study identified suitable crosses for accumulation of endosperm and amino acids modifiers. QPM inbreds with desirable modifications identified here would serve as suitable donor for both opaque2 and modifier loci in the marker-assisted backcross breeding. Further, contrasting inbreds can be used for generating mapping populations to identify new modifier loci underlying both endosperm and amino acids modifications.
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    • "CA339 is a QPM inbred line derived from pool33, which is from CIMMYT, and selected by Maize Research Center of Institute of Crop Sciences of CAAS; and liao2345 is a normal elite Chinese inbred line, cultivated by Maize Research Institute of Liaoning Academy of Agricultural Sciences. Two o2 NILs, liao2345/o2-1 and liao2345/o2-2, were selected from the two parents by MAS [21]. The pedigree and detailed information refer to Table 1. "
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    ABSTRACT: The recessive opaque-2 mutant gene (o2) reduces α-zeins accumulation in maize endosperm, changes the amino acid composition of maize kernels, induces an opaque endosperm, and increases the lysine content of kernels. The quality protein maize (QPM) inbred line CA339 (o2o2) and an elite normal inbred line liao2345 (O2O2) were used to construct o2 near-isogenic lines (NILs) by marker-assisted selection (MAS) using the co-dominant SSR marker phi057. Two specific o2 NILs were constructed, named liao2345/o2-1 and liao2345/o2-2. However, the kernel phenotypes of the two o2 NILs were different from each other. liao2345/o2-1 had the wild-type vitreous endosperm, which is similar to its recurrent parent liao2345, while the endosperm of liao2345/o2-2 was opaque, identical to typical o2 mutant individuals. In comparison to their recurrent parent liao2345, the lysine concentration of liao2345/o2-1 was similar and the lysine concentration in liao2345/o2-2 was doubled. SDS-PAGE analysis indicated that liao2345/o2-1 had the same zeins ratio as liao2345, whereas the zeins concentration of liao2345/o2-2 was markedly lower. Sequence and transcript abundance analyses indicated that the CDS of two o2 NILs are derived from CA339, but they have different promoters. The O2 transcript of liao2345/o2-2 is largely inhibited because of an rbg transposable element inserted between the TATA box and initiator codon of liao2345/o2-2. We concluded that different crossing-over patterns during the process of o2 NIL construction resulted in the different kernel phenotypes of the two o2 NILs. We surmise that the reversion of liao2345/o2-1 to wild type was due to the recombination with the wild type liao2345 promoter during introgression and backcrossing. The o2 mutant gene of donor (CA339) is a null mutant because of low O2 expression. However, its CDS probably encodes a protein with normal function which can maintain the normal accumulation of zeins in maize endosperm.
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