Conserved simple sequence repeats for the Limnanthaceae (Brassicales).

The Limnanthaceae (Order Brassicales) is a family of 18 taxa of Limnanthes (meadowfoam) native to California, Oregon, and British Columbia. Cultivated meadowfoam ( L. alba Benth.), a recently domesticated plant, has been the focus of research and development as an industrial oilseed for three decades. The goal of the present research was to develop several hundred simple sequence repeat (SSR) markers for genetic mapping, molecular breeding, and genomics research in wild and cultivated meadowfoam taxa. We developed 389 SSR markers for cultivated meadowfoam by isolating and sequencing 1,596 clones from L. alba genomic DNA libraries enriched for AG(n) or AC(n) repeats, identifying one or more unique SSRs in 696 clone sequences, and designing and testing primers for 624 unique SSRs. The SSR markers were screened for cross- taxa utility and polymorphisms among ten of 17 taxa in the Limnanthaceae; 373 of these markers were polymorphic and 106 amplified loci from every taxon. Cross-taxa amplification percentages ranged from 37.3% in L. douglasii ssp. rosea (145/389) to 85.6% in L. montana (333/389). The SSR markers amplified 4,160 unique bands from 14 genotypes sampled from ten taxa (10.7 unique bands per SSR marker), of which 972 were genotype-specific. Mean and maximum haplotype heterozygosities were 0.71 and 0.90, respectively, among six L. alba genotypes and 0.63 and 0.93, respectively, among 14 genotypes (ten taxa). The SSR markers supply a critical mass of high-throughput DNA markers for biological and agricultural research across the Limnanthaceae and open the way to the development of a genetic linkage map for meadowfoam ( x = 5).

The characterization of a mitochondrial acyl carrier protein isoform isolated from Arabidopsis thaliana.

A cDNA clone was isolated from an Arabidopsis leaf cDNA library that shared a high degree of protein sequence identity with mitochondrial acyl carrier proteins (mtACPs) isolated from Neurospora crassa and bovine heart muscle. The cDNA encoded an 88-amino acid mature protein that was preceded by a putative 35-amino acid presequence. In vitro protein import studies have confirmed that the presequence specifically targets this protein into pea mitochondria but not into chloroplasts. These studies indicated that pea mitochondria were not only able to import and process the precursor protein but also possessed the ability to acylate the mature protein. The mitochondrial localization of this protein, mtACP-1, was confirmed by western blot analysis. Arabidopsis mitochondrial protein extracts contained two cross-reacting bands that comigrated with the mature mtACP-1 and acylated mtACP-1 proteins. The acylated form of mtACP-1 was approximately 4 times more abundant than the unacylated form and appeared to be localized predominantly in the mitochondrial membrane where the unacylated mtACP-1 was present mostly in the matrix fraction. A chloroplast fatty acid synthase system was used, and mtACP-1 was able to function as a cofactor for fatty acid synthesis. However, predominantly short- and medium-chain fatty acids were produced in fatty acid synthase reactions supplemented with mtACP-1, suggesting that mtACP-1 may be causing premature fatty acid chain termination.

Primary structures of the precursor and mature forms of stearoyl-acyl carrier protein desaturase from safflower embryos and requirement of ferredoxin for enzyme activity.

Stearoyl-acyl carrier protein (ACP) desaturase (EC 1.14.99.6) catalyzes the principal conversion of saturated fatty acids to unsaturated fatty acids in the synthesis of vegetable oils. Stearoyl-ACP desaturase was purified from developing embryos of safflower seed, and extensive amino acid sequence was determined. The amino acid sequence was used in conjunction with polymerase chain reactions to clone a full-length cDNA. The primary structure of the protein, as deduced from the nucleotide sequence of the cDNA, includes a 33-amino-acid transit peptide not found in the purified enzyme. Expression in Escherichia coli of a gene encoding the mature form of stearoyl-ACP desaturase did not result in an altered fatty acid composition. However, active enzyme was detected when assayed in vitro with added spinach ferredoxin. The lack of significant activity in vitro without added ferredoxin and the lack of observed change in fatty acid composition indicate that ferredoxin is a required cofactor for the enzyme and that E. coli ferredoxin functions poorly, if at all, as an electron donor for the plant enzyme.