Identification and molecular characterization of shrunken-2 cDNA clones of maize.

Abstract

Mutation at the shrunken-2 (Sh2) locus of maize, a gene described more than 40 years ago, greatly reduces starch levels in the endosperm through its effect on the starch synthetic enzyme ADP-glucose pyrophosphorylase, an enzyme thought to be regulatory in this biosynthetic pathway. Although our previous work has suggested that Sh2 is a structural gene for this enzyme, we have also reported data compatible with Sh2 acting post-transcriptionally.In this study, we took advantage of a transposable element-induced Sh2 allele, its progenitor, and revertants to identify a clone for this locus. Although the cloning and identification were done independently of any knowledge concerning the product of this gene, examination of the deduced amino acid sequence revealed much similarity to known ADP-glucose pyrophosphorylase subunits of plants and bacteria, including regions involved in substrate binding and activator binding. Little sequence similarity, however, was found at the DNA level. These obsenrations provide direct evidence that Sh2 encodes a subunit for endosperm ADP-glucose pyrophosphorylase. Analysis of several phenotypically wild-type alleles arising from a mutable sh2-Ds allele revealed one unexpected case in which DNA sequences of Sh2 were rearranged in comparison with the progenitor Sh2. In contrast to wild type, the Dsinduced sh2 allele conditions at least two transcripts in the endosperm.

Maize Genes Encoding the Small Subunit of ADP- Glucose Pyrophosphorylase

“…Cloning and sequencing of Sh2 and Bt2 and analysis of informative mutants (Bae et al, 1990, Bhave et al, 1990) of maize endosperm transcripts and genes showed that both loci encode subunits of AGP. Bt2 encodes the small subunit, whereas the large subunit is derived from Sh2.…”

High level accumulation of α-glucan in maize kernels by expressing the gtfD gene from Streptococcus mutans

“…Sh2 encodes a subunit of endosperm ADP-glucose pyrophosphorylase, the key enzyme for starch biosynthesis in maize endosperm (Bhave et al 1990). Mutations in Sh2 result in a great reduction in starch levels with concomitantly high sucrose accumulation.…”

A New Twist on Transposons

“…Lal et al (2003) found the Helitron -like element within the Shrunken2 ( Sh2 ) gene in the mutant sh2-7527 , which appears to have arisen spontaneously in a conventional maize breeding program in the 1970s. sh2 mutants are characterized by kernels with poorly developed, shrunken endosperm tissue (Figure 1), resulting from mutations in the Sh2 gene, which encodes the large subunit of ADP-Glc pyrophosphorylase (Bhave et al, 1990). The Sh2 protein is a key enzyme in starch biosynthesis and is produced exclusively in the endosperm; sh2 mutants contain a much lower concentration of starch and a much higher concentration of Suc than the wild type.…”