opaque-2 modifiers increase gamma-zein synthesis and alter its spatial distribution in maize endosperm.

Geetha, K.; Lending, Craig R.; Lopes, M. A.; Wallace, John C.; Larkins, Brian A.

doi:10.1105/tpc.3.11.1207

Cited by 109 publications

(87 citation statements)

References 23 publications

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“…As shown in Fig. 2, the normal background CM105+ exhibited round and discrete PBs, although CM105o2 developed PBs with dramatically reduced density and size ( (21). This result could be further confirmed under scanning electron microscopy observation ( Fig.…”

Section: Transmission Electron Microscopy Of Endosperm From γRnai In supporting

confidence: 70%

“…The embryo of each individual was saved to extract genomic DNA for genotyping (Materials and Methods). PCR results showed that kernels 4,5,7,8,10,11,13,17,18,19,21,23,24, and 25 inherited the γRNAi gene (14 of 26 kernels) (Materials and Methods). As expected, the phenotypes of the zein accumulation patterns exhibited Mendelian segregation.…”

Section: Resultsmentioning

confidence: 99%

“…Although their molecular identities have remained unknown, QTLs could be correlated with observed increases in 27-kDa γ-zein transcript and protein in QPM (21). Unlike the 22-kDa α-zein genes, the 27-kDa γ-zein gene is not under the transcriptional control of the O2 protein (22,23).…”

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confidence: 89%

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γ-Zeins are essential for endosperm modification in quality protein maize

Holding

Messing

2010

Proc. Natl. Acad. Sci. U.S.A.

130

117

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Essential amino acids like lysine and tryptophan are deficient in corn meal because of the abundance of zein storage proteins that lack these amino acids. A natural mutant, opaque 2 (o2) causes reduction of zeins, an increase of nonzein proteins, and as a consequence, a doubling of lysine levels. However, o2's soft inferior kernels precluded its commercial use. Breeders subsequently overcame kernel softness, selecting several quantitative loci (QTLs), called o2 modifiers, without losing the high-lysine trait. These maize lines are known as "quality protein maize" (QPM). One of the QTLs is linked to the 27-kDa γ-zein locus on chromosome 7S. Moreover, QPM lines have 2-to 3-fold higher levels of the 27-kDa γ-zein, but the physiological significance of this increase is not known. Because the 27-and 16-kDa γ-zein genes are highly conserved in DNA sequence, we introduced a dominant RNAi transgene into a QPM line (CM105Mo2) to eliminate expression of them both. Elimination of γ-zeins disrupts endosperm modification by o2 modifiers, indicating their hypostatic action to γ-zeins. Abnormalities in protein body structure and their interaction with starch granules in the F1 with Mo2/+; o2/o2; γRNAi/+ genotype suggests that γ-zeins are essential for restoring protein body density and starch grain interaction in QPM. To eliminate pleiotropic effects caused by o2, the 22-kDa α-zein, γ-zein, and β-zein RNAis were stacked, resulting in protein bodies forming as honeycomb-like structures. We are unique in presenting clear demonstration that γ-zeins play a mechanistic role in QPM, providing a previously unexplored rationale for molecular breeding.electron microscopy | stacking of RNAi events | storage organs | opaque phenotype | kernel hardness G rain hardness is a key agronomic trait in maize (Zea mays L.)because it provides resistance to damage during harvesting and marketing, as well as to insect and fungal damage. Kernel texture is determined by the relative amounts of hard (vitreous) and soft (opaque) endosperm and there is a positive correlation between zein storage proteins and kernel vitreousness (1). Zeins are a heterogeneous mixture of alcohol-soluble proteins, falling into four classes based on their structure (α-, β-, γ-, and δ-zeins) (2). The zeins extracted with the Osborne method (3) are classified as z1 (19-and 22-kDa α-zeins) and the cross-linked z2 group (50-, 27-, and 16-kDa γ-zeins, 15-kDa β-zein, and 18-and 10-kDa δ-zeins) (4, 5). Zeins are deposited in rough endoplasmic reticulum-delimited protein bodies (PBs) in endosperm cells from around 10 d after pollination (DAP) (6, 7). Alpha-and δ-zeins are mainly stored in the center of PBs, and γ-and β-zeins are deposited in the peripheral region (8). The Cys-rich γ-and β-zeins have redundant function in the stabilization of PB morphology (9). The translucency (vitreousness) of the mature kernel is influenced by PB composition and the spatial organization of α-, β-, γ-, and δ-zeins (10-16).Because zeins are essentially devoid of lysine and tryptophan, their high-lev...

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Section: Transmission Electron Microscopy Of Endosperm From γRnai In supporting

confidence: 70%

Section: Resultsmentioning

confidence: 99%

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γ-Zeins are essential for endosperm modification in quality protein maize

Holding

Messing

2010

Proc. Natl. Acad. Sci. U.S.A.

130

117

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“…The gene encodes an ACS-like enzyme that we predict to play a key role in membrane biogenesis, altering the structure of the PBs, which, in turn, cause the nonvitreous phenotype. The PBs of o7, with their striking invaginations, have a unique phenotype among the other opaque mutants studied so far, which were either small, misshapen, irregularly lobed, or reduced in number (Geetha et al 1991;Dannenhoffer et al 1995;Coleman et al 1997;Kim et al 2004Kim et al , 2006. Also unique is the type of gene causing the phenotype.…”

Section: Discussionmentioning

confidence: 99%

The Maize High-Lysine Mutantopaque7Is Defective in an Acyl-CoA Synthetase-Like Protein

Miclaus

et al. 2011

Genetics

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Maize (Zea mays) has a large class of seed mutants with opaque or nonvitreous endosperms that could improve the nutritional quality of our food supply. The phenotype of some of them appears to be linked to the improper formation of protein bodies (PBs) where zein storage proteins are deposited. Although a number of genes affecting endosperm vitreousness have been isolated, it has been difficult to clone opaque7 (o7), mainly because of its low penetrance in many genetic backgrounds. The o7-reference (o7-ref) mutant arose spontaneously in a W22 inbred, but is poorly expressed in other lines. We report here the isolation of o7 with a combination of map-based cloning and transposon tagging. We first identified an o7 candidate gene by map-based cloning. The putative o7-ref allele has a 12-bp in-frame deletion of codons 350-353 in a 528-codon-long acyl-CoA synthetase-like gene (ACS). We then confirmed this candidate gene by generating another mutant allele from a transposon-tagging experiment using the Activator/Dissociation (Ac/Ds) system in a W22 background. The second allele, isolated from 1 million gametes, presented a 2-kb Ds insertion that resembles the single Ds component of double-Ds, McClintock's original Dissociation element, at codon 496 of the ACS gene. PBs exhibited striking membrane invaginations in the o7-ref allele and a severe number reduction in the Ds-insertion mutant, respectively. We propose a model in which the ACS enzyme plays a key role in membrane biogenesis, by taking part in protein acylation, and that altered PBs render the seed nonvitreous. SEEDS are the most important source of essential amino acids. In cereals, they are mainly stored in the endosperm rather than the embryo of the seed. They accumulate in proteins, also called storage proteins, which are deposited in subcellular structures, called protein bodies (PBs). Because these proteins, called zeins in maize, account for 50-70% of the total protein, their amino acid composition determines the nutritional value of the seed. Their proper deposition inside PBs confers the normal vitreous phenotype to the endosperm. PBs are specialized endosperm organelles that form as an extension of the membrane of the rough endoplasmic reticulum (RER), into which zeins are secreted as the signal peptide is processed. Zeins are classified on the basis of their structure into a-, b-, g-, and d-zeins and appear to function and localize differentially during the maturation of PBs. Subclasses were defined for each of them on the basis of their relative molecular weights: 19-and 22-kDa a-zeins, 15-kDa b-zein, 16-, 27-, and 50-kDa g-zeins, and 10-and 18-kDa d-zeins. After being secreted into the RER, the b-and g-zeins form a matrix, which is penetrated by the a-and d-zeins, enlarging the PB and making it a spherical structure of 1-2 mm (Lending and Larkins 1989). Alterations in size, shape, or number of PBs generally determine the opaque phenotype (Holding and Larkins 2009), the sole exception being floury1 (fl1), an opaque mutant with no alteratio...

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“…Successful development of QPM requires introgression of o2 while selecting for suitable genetic modifier background to guarantee the development of high quality vitreous kernels. Genetic analysis of o2 modifiers has led to the identification of loci that affect packaging of starch granules in grain (Lopes et al, 1995;Gibbon et al, 2003) and alternation of zein proteins critical for modification (Geetha et al, 1991;Lopes and Larkings 1991). Although their molecular identities have remained unknown, these modifier loci are correlated with increases in 27-kDa γ-zein transcript and protein in QPM (Geether et al, 1991).…”

Section: Introductionmentioning

confidence: 99%

Feasibilty of zein proteins, simple sequence repeats and phenotypic traits for background selection in quality protein maize breeding

Maphosa¹,

Oballim²,

Nalukenge³

et al. 2011

African Crop Science Journal

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Widespread adoption of quality protein maize (QPM), especially among tropical farming systems has been slow mainly due to the slow process of generating varieties with acceptable kernel quality and adaptability to different agroecological contexts. A molecular based foreground selection system for opaque 2 (o2), the cause of enhanced lysine content in maize exists. Background selection systems albeit, are poorly developed in spite of the mapping of putative loci associated with kernel modification and knowledge on causes of modification. The aim of this study was to develop background selection systems for o2 introgression into locally adapted genotypes. Experiments were conducted at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK), in Uganda on backcross progeny (BC1F1) and BC2F2), derived from a locally adapted line 136R and a QPM donor CML176. We tested the use of zein proteins known to influence modification as well as DNA markers and phenotypic descriptors as tools for background selection for recurrent parent genome and modifier loci in locally adapted maize genotypes. Simply inherited traits such as maize streak virus disease resistance were suitable for background selection. Other traits include plant and ear heights. The simple sequence repeats markers mapped to chromosomes 3, 5, 7, respectively and associated with quantitative trait loci (QTL) conditioning resistance in maize to grey leaf spot and anthesis to silking interval were suitable for assay of recurrent parent genome. The 27-kDa γ zein protein levels was suitable for background selection for kernel modification. It should, however, be used along with other zeins such as the 22 kDa and 19 kDa zein proteins.

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opaque-2 modifiers increase gamma-zein synthesis and alter its spatial distribution in maize endosperm.

Cited by 109 publications

References 23 publications

γ-Zeins are essential for endosperm modification in quality protein maize

γ-Zeins are essential for endosperm modification in quality protein maize

The Maize High-Lysine Mutantopaque7Is Defective in an Acyl-CoA Synthetase-Like Protein

Feasibilty of zein proteins, simple sequence repeats and phenotypic traits for background selection in quality protein maize breeding

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