Interaction of maize mutants floury-2 and opaque-7 with opaque-2 in the synthesis of endosperm proteins

Fonzo, N. di; Fornasari, E.; Salamini, F.; Reggiani, Remo; Soave, C.

doi:10.1093/oxfordjournals.jhered.a109394

Cited by 47 publications

(14 citation statements)

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Section: Introductionmentioning

confidence: 65%

“…Protein bodies in o2 and fl2 endosperm are smaller than normal, but fl2-encoded protein bodies are asymmetrical and misshapen compared to the spherical protein bodies of normal and o2 endosperm (6). The zein protein profile and the morphology of the protein bodies in o2ff2 double mutants more closely resemble those found in o2 alone, indicating that o2 is epistatic to fl2 (7,8).The 02 gene has been isolated and shown to encode a leucine zipper-type transcription factor that controls expression of the 22-kDa family of a-zein genes (9), but the basis of thefl2 defect is unknown.The fl2 mutation is associated with enhanced levels of binding protein (BiP), the 75-kDa endoplasmic reticulum (ER) molecular chaperone, that becomes localized near the periphery of ER-derived protein bodies (10-13). Only onefl2 allele has been identified (14), and this, taken together with its semidominant pattern of inheritance, suggests that it is a unique gain-of-function mutation.…”

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confidence: 99%

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A defective signal peptide in the maize high-lysine mutant floury 2.

Coleman

Lopes

Gillikin

et al. 1995

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

118

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The maize floury 2 (/72) mutation enhances the lysine content of the grain, but the soft texture of the endosperm makes it unsuitable for commercial production. The mutant phenotype is linked with the appearance of a 24-kDa a-zein protein and increased synthesis of binding protein, both of which are associated with irregularly shaped protein bodies. We have cloned the gene encoding the 24-kDa protein and show that it is expressed as a 22-kDa a-zein with an uncleaved signal peptide. Comparison of the deduced N-terminal amino acid sequence of the 24-kDa a-zein protein with other a-zeins revealed an alanine to valine substitution at the C-terminal position of the signal peptide, a histidine insertion within the seventh a-helical repeat, and an alanine to threonine substitution with the same a-helical repeat of the protein. Structural defects associated with this a-zein explain many of the phenotypic effects of the fl2 mutation.Between 50% and 60% of the protein in maize (Zea mays L.) kernels consists of a mixture of prolamin storage proteins known as zeins. These proteins are rich in proline and glutamine but lack lysine, making the seed nutritionally inferior for monogastric animals. The lysine deficiency of maize spurred extensive efforts to identify mutants with higher levels of this essential amino acid. Thirty years ago the opaque 2 (o2) and floury 2 (f72) mutants were shown to have elevated levels of lysine in the endosperm protein (1, 2). These observations generated a great deal of optimism regarding the potential development of high-lysine corn, but the soft, starchy endosperm of these mutants causes the kernels to be susceptible to mechanical damage and creates a higher susceptibility to insect and fungal damage. Consequently, neither mutant gained wide commercial application.Despite their phenotypic similarities, distinctive biochemical differences distinguish o2 andfl2 mutants. The o2 mutation is recessive, while the fl2 mutation is semidominant, with the severity of the phenotype correlated to the dosage of the mutant allele. Both mutants exhibit reduced zein accumulation in the endosperm, but the o2 mutation specifically affects the 22-kDa a-zeins (3), while the fl2 mutation equally affects synthesis of all classes of zeins (4, 5). Protein bodies in o2 and fl2 endosperm are smaller than normal, but fl2-encoded protein bodies are asymmetrical and misshapen compared to the spherical protein bodies of normal and o2 endosperm (6). The zein protein profile and the morphology of the protein bodies in o2ff2 double mutants more closely resemble those found in o2 alone, indicating that o2 is epistatic to fl2 (7,8).The 02 gene has been isolated and shown to encode a leucine zipper-type transcription factor that controls expression of the 22-kDa family of a-zein genes (9), but the basis of thefl2 defect is unknown.The fl2 mutation is associated with enhanced levels of binding protein (BiP), the 75-kDa endoplasmic reticulum (ER) molecular chaperone, that becomes localized near the periphery of ER-derived ...

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Section: Introductionmentioning

confidence: 65%

mentioning

confidence: 99%

A defective signal peptide in the maize high-lysine mutant floury 2.

Coleman

Lopes

Gillikin

et al. 1995

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

118

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“…The widely studied opaque-2 (o2) mutant acts to preferentially reduce the 21-22 kDa class of zein polypeptides [22]. The 02 gene has been isolated by transposon tagging [47] and nucleotide sequence analysis suggests that the 02 protein is a transcriptional activator [33].…”

Section: Discussionmentioning

confidence: 99%

The effect of different alleles at the r locus on the synthesis of seed storage proteins in Pisum sativum

Turner

Barratt²,

Casey

1990

Plant Mol Biol

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Rocket immunoelectrophoresis was used to measure the accumulation of storage proteins in developing cotyledons of two Pisum sativum (pea) genotypes, that were close to isogenic except for the nature of the allele at the r locus. There was a marked decrease in legumin accumulation in the rr (wrinkled-seeded) genotype compared to the RR (round-seeded) genotype. The accumulation of vicilin did not differ greatly between the two genotypes. Pulse-labelling studies indicated that the differences in rates of accumulation of legumin between the rr and RR genotypes were a consequence of differences in rates of protein synthesis. Measurements of relative amounts of specific mRNAs, using cDNA clones as probes, showed lower amounts of legumin mRNA in developing cotyledons of the rr, compared to the RR, genotype. Both vicilin mRNAs and convicilin mRNA, the latter of which shows a similar temporal pattern of expression to those of the major legumin species, are relatively unaffected by the nature of the allele at the r locus. Nuclear run-on transcription experiments indicated no differences in the rate of synthesis of legumin transcripts in the rr and RR near-isolines. The consequences of homozygosity for the r allele on storage protein mRNA levels in vitro may be mimicked by manipulating the sucrose concentration of the culture medium.

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“…However, the peculiar feature of zein is the broad scattering of its genes in the genome [16,191 (and Viotti et a]., unpublished). As the various zein polypeptides are synchronously accumulated during the endosperm development [2,59,64], the expression of zein genes might be under the control of cisltrans-acting and integrated regulatory elements. The presence of various loci on different chromosomes, acting in different ways on the synthesis of the zein components and found to be physically linked to zein structural genes [lo?…”

Section: Discussionmentioning

confidence: 99%

Genes and mRNAs Coding for Zein Polypeptides in Zea mays

Viotti¹,

Sala²,

Marotta³

et al. 1979

Eur J Biochem

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Zein messenger RNAs from maize endosperm were purified by successive oligo(dT)-cellulose chromatography and sucrose gradient centrifugation. Polyacrylamide gel electrophoresis under denaturating conditions revealed the presence of two size classes of zein messenger RNAs of M , 3.5 x lo5 and 4.10 x lo5. The mRNA was shown to synthesize the major zein polypeptides, to have a base composition characteristic of a poly(A)-containing RNA and to be transcribed by reverse transcriptase into complementary DNA. The yo t l j z of the hybridization curve of cDNA hybridized to an excess of mRNA was shown to be 7 x l o p L M . s indicating that about 15 non-cross-hybridizing sequences are present in the zein mRNA preparations. The kinetics of cDNA annealing with an excess of maize DNA from 2n cells suggest a ten-times reiteration of each mRNA sequence. This result is confirmed from saturation experiments, where in cDNA excess to DNA, the number of zein genes per haploid maize genome was estimated as about 120 copies. Similar experiments carried out on DNA from normal and mutant endosperms (3n cells) indicate the absence of large amplifications or deletions of zein genes in the tissue devoted to zein synthesis.During development, maize endosperm accumulates a large amount of storage proteins [1,2]. The main protein fraction is zein, a hydrophobic protein synthesized by membrane-bound polysomes and stored in granules (protein bodies) [3 -51.The hydrophobicity of zein is due to its high level of neutral and hydrophobic amino acid residues (more than 90%) and to the low level of basic amino acids such as lysine, which also contribute to the low biological value of maize seed proteins [6-111. As shown by dodecylsulfate electrophoresis, zein consists of between three and five major polypeptides in the 22 700 -19 000 molecular weight range and some minor components of M , 16000-14000 [12,13]. A wider heterogeneity (8-15 components) can be obtained by urea/acrylamide gel electrophoresis [14,15] or by isoelectric focusing [I 21. Bidimensional analysis (isoelectric focusing/dodecylsulfate electrophoresis) shows that some of the isoelectric-focusing zein bands behave as single polypeptides, while others can be further resolved into two or three components [16]. Altogether, the data indicate that zein is fractionable into at least 20-25 polypeptides [17,18]. The isoelectric-focusing pattern of zein was shown to be genotype-specific [8, 121 and not due to post-translational modifications [5]. Moreover, genetic studies have demonstrated that the zein isoelectric-focusing components behave as direct products of structural genes [19]. In order to establish the molecular basis for such a wide heterogeneity and to obtain further data on the genetic system controlling zein synthesis, we studied by molecular hybridization the complexity of zein messenger RNAs and the number of zein genes in the maize genome. MATERIALS AND METHODS MaterialsMaize seeds obtained 21 days after pollination, from the inbred line W64A grown in the field, were harvest...

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Interaction of maize mutants floury-2 and opaque-7 with opaque-2 in the synthesis of endosperm proteins

Cited by 47 publications

References 0 publications

A defective signal peptide in the maize high-lysine mutant floury 2.

A defective signal peptide in the maize high-lysine mutant floury 2.

The effect of different alleles at the r locus on the synthesis of seed storage proteins in Pisum sativum

Genes and mRNAs Coding for Zein Polypeptides in Zea mays

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