Analysis of Maize Brittle-1 Alleles and a Defective Suppressor-Mutator-Induced Mutable Allele

Abstract

A mutant allele of the maize brittle-7 ( b t l ) locus, brittle-l-mutable (btl-m), was shown genetically and molecularly to result from the insertion of a defective Suppressor-mutator (dSpm) transposable element. An Spm-hybridizing restriction enzyme fragment, which cosegregates with the btl-m allele and is absent from wild-type revertants of btl-m, was identified and cloned. Non-Spm portions of it were used as probes to identify wild-type ( B t l ) cDNAs in an endosperm library. The 4.3-kb btl-m genomic clone contains a 3.3-kb dSpm, which is inserted in an exon and is composed of Spm termini flanking nonQpm sequences. RNA gel blot analyses, using a cloned Btl cDNA probe, indicated that Btl mRNA is present in the endosperm of developing kernels and is absent from embryo or leaf tissues. Several transcripts are produced by btl-m. The deduced translation product from a 1.7-kb Btl cDNA clone has an apparent plastid transit peptide at its amino terminus and sequence similarity to severa1 mitochondrial innerenvelope translocator proteins, suggesting a possible role in amyloplast membrane transport.

Identification by bacterial expression and functional reconstitution of the yeast genomic sequence encoding the mitochondrial dicarboxylate carrier protein

“…With the exception of the phosphate and citrate carriers in mammals [4,6], but not in yeast [15,16], the mitochondrial carrier proteins do not have N-terminal extensions that are removed during entry to the organelle, and none is associated with xii-C1. However, with the possible exceptions of the maize brittlel protein [37]and the PMP-47 protein from Candida boidinii [38], the characterised members of this family of carriers have been found exclusively in mitochondrial membranes. Therefore, this is the most likely sub-cellular localisation of xii-C1.…”

ADP-glucose drives starch synthesis in isolated maize endosperm amyloplasts: characterization of starch synthesis and transport properties across the amyloplast envelope

“…(3) Beside the plastid ATP\ADP transporter, a second inner envelope protein has been identified that probably represents the plastid ADPGlc transporter. Molecular analysis of the maize brittle1 mutation clearly shows that this gene encodes an innerenvelope membrane protein with significant homology to several mitochondrial transporters [39,40]. Moreover, since ADPGlc concentration in maize endosperm tissues from brittle1 mutants is several times higher than in the wild-type, an involvement of the Brittle1 protein in ADPGlc transport is strongly indicated [41].…”

Most of ADP·glucose linked to starch biosynthesis occurs outside the chloroplast in source leaves

“…9, which is published as supporting information on the PNAS web site). Those proteins share high homology to Brittle-1, a well characterized ADPG translocator occurring in the amyloplasts of maize endosperms (58,60,61). (iii) A cytosolic glucan synthase occurs in the cytosol of leaves that utilizes ADPG as the sugar-donor molecule (62).…”