Arrested Embryos from the bio1 Auxotroph of Arabidopsis thaliana Contain Reduced Levels of Biotin

Abstract

The biol auxotroph of Arabidopsis thaliana is a recessive embryonic lethal that forms normal plants in the presence of biotin. The purpose of this study was to determine whether aborted seeds produced by heterozygous plants grown without vitamin supplements contained reduced levels of biotin. Two methods were used to determine the biotin content of mutant and wild-type tissues: streptavidin binding in microtiter plates and growth of the biotin-requiring bacterium Lactobacillus plantarum.Total biotin was measured in extracts prepared from immature seeds prior to desiccation. Aborted seeds produced by heterozygous (biol/BIO1) plants contained some biotin in the maternal seed coat but virtually no detectable biotin in the arrested embryo. This lack of biotin was not observed in arrested embryos from other mutants with similar patterns of abnormal development. These results are consistent with the model that biol tissues are defective in biotin synthesis. The alternative model of increased degradation is inconsistent with the recessive nature of the mutation and the ability of rescued plants to continue growing for several weeks following removal of supplemental biotin.

An Embryo-Defective Mutant of Arabidopsis Disrupted in the Final Step of Biotin Synthesis

“…Analysis of this mutant allowed the disrupted step to be identified and suggested that the biotin pathway might be conserved between plants and bacteria (Shellhammer and Meinke, 1990;Patton et al, 1996b). Further interpretation of the mutant phenotype was limited by the availability of a single mutant allele of unknown strength.…”

“…Heterozygous plants were subsequently grown in 16-/8-h light/dark cycles and identified by screening immature siliques for defective seeds (Heath et al, 1986;Meinke, 1994). Isolation and characterization of the bio1 auxotroph, known originally as mutant 122G-E, was described by Meinke (1985), Schneider et al (1989), and Shellhammer and Meinke (1990). The bio1-1 allele used here was isolated following ethyl methanesulfonate seed mutagenesis of ecotype Columbia.…”

“…The bio1 mutant was the first plant auxotroph shown to result in embryo lethality (Schneider et al, 1989). Mutant bio1 embryos remain pale throughout development, typically arrest between the heart and cotyledon stages of embryogenesis, contain severely reduced levels of biotin, and can be rescued by biotin, dethiobiotin, or 7,8-diaminopelargonic acid (Shellhammer and Meinke, 1990). The initial model that this mutant was defective in the conversion of 7-keto-8-aminopelargonic acid to 7,8-diaminopelargonic acid (Shellhammer, 1991) has recently been confirmed by demonstrating that mutant plants can be rescued by introduction of a functional copy of the bioA gene of E. coli through Agrobacterium-mediated transformation (Patton et al, 1996b).…”

Mapping genes essential for embryo development in Arabidopsis thaliana

“…The latter mutant was subsequently shown to require biotin for normal growth ). Shellhammer and Meinke (1990) then showed that arrested embryos from heterozygous 122G-E (biol) plants contained 5-fold less biotin than corresponding wild-type embryos. Recent work on biol has dealt with determining the biochemical defect in this mutant.…”

7-Keto-8-Aminopelagonic Acid Synthase as a Potential Herbicide Target

“…Mutant bio1, first plant auxotroph for biotin, has shown to result in embryonic lethality, and its embryos remain pale throughout development, typically arrested between germination and cotyledon stage of embryogenesis (Alban et al, 2000, Meinke, 1985. Plant growth was rescued by biotin, dethiobiotin, or DAPA, but KAPA supply, or by genetic complementation by E. coli bioA gene coding DAPA aminotransferase, demonstrating that mutant plants are defective in this enzyme (Alban et al, 2000;Meinke, 1985;Shellhammer and Meinke, 1990;Patton et al, 1996;. Based on feeding studies, Shellhammer and Meinke (1990) suggested that bio 1 was defective in the conversion of KAPA to DAPA, the enzymatic function of the BioA protein of E. coli.…”