Abstract
The Opaque-2 (O2) gene encodes a transcriptional activator specifically expressed for grain development of maize. o2 mutants have an opaque and chalky kernel, with a decrease in zein storage protein content, and an increase in the proportions of lysine and tryptophan. In this review, we present recent results investigating genetic properties of the O2 network, using transcriptome and proteome approaches, associated with measurements of activities of enzymes of the aspartate pathway and lysine degradation. The structural polymorphism at the O2 locus was investigated by RFLP in a collection of 51 maize inbred lines. Most polymorphic sites were found outside the coding regions. We then searched for relationships between RFLP polymorphism and (i) mRNA abundance of O2 and of known or suspected target genes, (ii) activity of SDH and (iii) amount of zein isoforms. Polymorphic restriction sites in the 5' upstream regions of the O2 gene were found associated with O2 mRNA abundance (three sites) and the amount of two 19 kDa alpha-zein isoforms (two sites). One restriction site on the 3' side of the O2 gene was found associated with Lor/Sdh mRNA abundance. Our results indicate relationships between polymorphism at the O2 locus and the expression of some of its target genes. Evidence of these associations has to be confirmed on larger samples, and the analysis of the O2 gene sequence should allow more precise testing of the actual involvement of O2 polymorphism in its own transcriptional expression, and in the expression of its target genes.
Highlights
Introduction to the Opaque2 regulatory network The recessive opaque-2 (o2) mutation of maize gives an opaque character to the usually translucent mature kernel, but has many pleiotropic effects
Structural gene polymorphism of O2 and the expression of several potential target genes were analyzed in a collection of 51 genetically diversified maize lines, with different kernel types (Table 1)
The variability of mRNA abundance was analyzed for cyPpdk, Lor/Sdh and the acetohydroxy acid synthase gene (Ahas)
Summary
Introduction to the Opaque2 regulatory network The recessive opaque-2 (o2) mutation of maize gives an opaque character to the usually translucent mature kernel, but has many pleiotropic effects. Evidence has been obtained that the enzyme dihydrodipicolinate synthase (DHDPS), which is the first enzyme of the lysine branch in the biosynthesis pathway, might be down-regulated by O2, since the o2 mutant exhibited much higher levels of DHDPS activity in the endosperm as compared to the wild-type
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