Mutant alleles that are altered in quantitative, organ‐specific behavior

Abstract

Three new mutant alleles of maize alcohol dehydrogenase-1 (Adhl) were recovered following ally1 alcohol selection of pollen. Each is altered in quantitative, organ-specific, regulatory properties. All mutant sites act in cis to the structural gene component. One mutant arose spontaneously, one followed indirectly from irradiation with high 2 accelerated particles, and one was induced by an autonomous mutator system. Each mutant is assessed in three organs by utilizing ADH allozyme ratios that were quantified at the level of ADH enzyme activity and either ['HI-Leu incorporation into newly synthesized ADHl subunits or direct protein determinations. One mutation simultaneously raises Adhl expression in one organ and lowers it in another, another affects expression in one organ only, and another is extremely underexpressed in all organs but is unstable. This unstable allele has generated derivative mutant alleles that have less or zero ADH expression. We do not yet know whether or not coding sequences are involved in these mutants. We conclude that information for organ specificity and quantitative behavior resides near or within Adhl coding sequences.

DNA insertion in the first intron of maize Adh1 affects message levels: cloning of progenitor and mutant Adh1 alleles.

“…ref. 6). Two "down" derivatives of AdhJ-S3034, S3034a (null), and S3034b (13% of wild-type Adh1-S activity) also have been studied.…”

“…The mutant allele, S3034, supports about 40% normal ADH1 translation rates, and is about 100 times more unstable genetically (at two revertants per 104 pollen grains) than ethyl methanesulfonate-induced mutants of Adhl-S (6). Mutant derivatives of S3034 were selected that express 13% and 0% ADH1 protein, and these quantitative alleles lowered expression in scutellum (of the seed), anaerobic root, and pollen to about the same extent (6). The availability of a cDNA probe for Adhl sequence allowed the demonstration that the low expression of S3034 and its derivative alleles reflected poly(A)+ RNA levels and that each allele carries a DNA insertion of about 1.5 kilobases (kb) just 5' to the region of genome recognized by the cDNA clone (5).…”

“…By using this ADH1 cDNA clone as a probe for the maize genome, it was found that Adhl may be identified on Southern blots as a single-copy gene (5). Among the several AdMl mutants that seem to alter regulatory rather than coding functions is a series of unstable quantitative alleles originating from a single mutant: Adhl-53034 (6). The mutant was selected as an allyl alcohol-resistant pollen grain shed from a genetically marked line carrying Robertson's mutator activity (7) and the Adhl-S target allele.…”

The Mu1 maize transposable element induces tissue-specific aberrant splicing and polyadenylation in two Adh1 mutants.

“…The next in-frame ATG resides in exon 2; its use would produce a truncated peptide lacking 34 amino acids from the N terminus. Analysis of alcohol dehydrogenase activity by native starch gel electrophoresis of S3034 extracts does not reveal the presence of this aberrant polypeptide (7,19), indicating that if this truncated protein is translated, it is inactive or unstable.…”

“…Freeling and co-workers devised a means of positive selection for impaired alcohol dehydrogenase activity. This protocol permitted isolation of a number of mutants exhibiting quantitative alterations in their expression (7); all carried Mul insertions in intron 1 of Adhl. Thus, Adhl-53034 (S3034) and AdhJ-S4477 (S4477) encode a protein indistinguishable from that produced by the IS progenitor allele but exhibit only 20 to 40% and 50 to 70%, respectively, of the ADHI enzymatic activity present in IS.…”