Differential expression of a gene for a methionine-rich storage protein in maize

Abstract

A methionine-rich 10 kDa zein storage protein from maize was isolated and the sequence of the N-terminal 30 amino acids was determined. Based on the amino acid sequence, two mixed oligonucleotides were synthesized and used to probe a maize endosperm cDNA library. A full-length cDNA clone encoding the 10 kDa zein was isolated by this procedure. The nucleotide sequence of the cDNA clone predicts a polypeptide of 129 amino acids, preceded by a signal peptide of 21 amino acids. The predicted polypeptide is unique in its extremely high content of methionine (22.5%). The maize inbred line BSSS-53, which has increased seed methionine due to overproduction of this protein, was compared to W23, a standard inbred line. Northern blot analysis showed that the relative RNA levels for the 10 kDa zein were enhanced in developing seeds of BSSS-53, providing a molecular basis for the overproduction of the protein. Southern blot analysis indicated that there are one or two 10 kDa zein genes in the maize genome.

The organization and expression of a maize ribosomal protein gene family.

“…Because we have determined relative rather than absolute transcript abundances, our data do not directly address this hypothesis. However, the data presented in Figure 5 indicate that the highest $14 transcript levels observed are much lower than those of the 10-kD ZAP, a relatively minor storage protein encoded by a single gene (Kirihara et al 1988). Another explanation for the maintenance of a multigene family is that different copies of the gene are regulated differently, allowing the plant to control the level of the $14 gene product independently in different cell types or developmental stages.…”

“…A qualitatively identical peak in S14 transcript levels was observed upon probing RNA blots of poly(A) + RNA from developing endosperm with the MCH1 probe (data not shown), demonstrating that the observed pattern of transcript accumulation is not an artifact of normalizing to rRNA levels. For comparison, a eDNA clone for the 10-kD methionine-rich zein-associated protein gene (10 kD ZAP, Rubenstein and Geraghty 1986;Kirihara et al 1988) was hybridized to the same endosperm RNA samples; this probe provides a marker for the onset of storage protein synthesis (Fig. 5).…”

“…All samples were normalized to the rRNA probe signal to minimize loading errors. The probes used were the S14 cDNA clone MCH1, a 10-kD ZAP cDNA (Kirihara et al 1988), and an EcoRI fragment containing the entire rDNA repeat {McMullen et al 1986). Note that the 10-kD ZAP data are presented on a different scale from the S14 data.…”

Coexpression of the maize delta-zein and beta-zein genes results in stable accumulation of delta-zein in endoplasmic reticulum-derived protein bodies formed by beta-zein.

“…Plasmid pMZEllOk containing the 6-zein cDNA isolated from a maize endosperm cDNA library (Kirihara et al, 1988) was a gift from J. Messing (Rutgers University, Piscatawax,. MJ)j.…”

“…The p-zein and y-zein proteins share regions of homology with other prolamins. 6-Zein has some sequence similarity with dicot storage proteins, such as the 2 s albumin of Brazil nut (Kirihara et al, 1988). a-Zeins, which are the most abundant, have a unique structure (Argos et al, 1982).…”