opaque-2 modifiers increase gamma-zein synthesis and alter its spatial distribution in maize endosperm.
Through the action of opaque-2 modifier genes, the soft, floury endosperm of opaque-2 mutants is converted to a vitreous phenotype. This change in endosperm texture is associated with a twofold to threefold increase in gamma-zein content. To investigate the effect of opaque-2 modifiers on the expression of gamma-zein genes, we analyzed the synthesis and distribution of gamma-zein protein and the level of gamma-zein mRNAs in developing endosperms of the inbreds W64A and W64Ao2, a modified opaque-2 mutant Pool 34 QPM, and their reciprocal F1 hybrids. We also characterized the number and organization of gamma-zein genes in these and related maize genotypes. Our studies show that opaque-2 modifiers are semidominant genes, resulting in a twofold to threefold increase in gamma-zein gene expression in both opaque-2 and normal genetic backgrounds. The increase in gene expression appears to be a consequence of enhanced mRNA transcription or stability rather than gene amplification because gamma-zein genes occur in one or two copies in modified as well as nonmodified genetic backgrounds. Ultrastructural studies showed that gamma-zein occurs in high concentrations in the first few subaleurone cells of nonmodified endosperms, but high concentrations of gamma-zein occur in the subaleurone and central endosperm cells of modified opaque-2 mutants. The increased concentration and distribution of gamma-zein in modified endosperms are highly correlated with the activity of opaque-2 modifier genes.
Geetha
K B
KB
Department of Plant Sciences, University of Arizona, Tucson 85721.
Lending
C R
CR
Lopes
M A
MA
Wallace
J C
JC
Larkins
B A
BA
D016253:Microscopy, Immunoelectron; D009154:Mutation; D010944:Plants / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014018:Tissue Distribution; D003313:Zea mays / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D015028:Zein / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism
D012333:RNA, Messenger; D015028:Zein