The protein quality of maize can be improved by replacing normal Opaque2
alleles with non-functional recessive alleles opaque2 (o2). The allele o2 produces a
severe phenotype with soft endosperm enhancing its protein quality but decreasing its
agronomical value. Plant breeders have restored a desirable ratio of hard to soft
endosperm in o2 germplasm known as Quality Protein Maize (QPM). Neither the
mechanism nor the genetic components by which the modification of the endosperm in
QPM lines occurs are well understood. To increase the understanding of the genetics of
endosperm modification, a population of 146 recombinant inbred lines derived from a
cross between the o2 inbred line B73o2 and the QPM inbred line CML161 was
evaluated in two Texas locations from 2004 to 2006. Four traits related to endosperm
texture were measured and showed significant effect of the inbred lines, high heritability
estimates and high genetic correlations. Relative content of the essential amino acids
lysine, tryptophan and methionine were measured and showed significant effects of the lines and considerable high genetic correlations and heritabilities. Negative correlation
was observed between endosperm texture traits and amino acid content. Quantitative
trait loci (QTL) were mapped for traits related to the modification of endosperm texture
and the content of lysine, tryptophan and methionine. QTLs clusters for endosperm
texture traits were detected on chromosomes 3, 5, 6 and 8 explaining 62-68% of the
variation. QTLs clusters for amino acid contents were located on chromosomes 7 and 8
that explained up to 39% of the observed variation. The product of the O2 gene is a
transcription factor that affects the expression of a number of endosperm genes. A group
of 29 endosperm genes associated with the O2 activity were evaluated in developing
endosperm of the recombinant inbred lines. Genomic regions controlling gene transcript
abundance in developing endosperm were identified by expression QTL mapping.
Evidence is presented of QTL hot spots that segregate in association with endosperm
texture modification or amino acid contents and are associated with the regulation of the
expression of a group of endosperm genes.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2551 |
| Date | 15 May 2009 |
| Creators | Gutierrez Rojas, Libardo Andres |
| Contributors | Menz, Monica, Pepper, Alan |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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