Showing papers by "Bonnie Bartel published in 2001"
TL;DR: Studies of the gain-of-function iaa28-1 mutant suggest that IAA28 normally represses transcription, perhaps of genes that promote lateral root initiation in response to auxin signals, and in contrast to other Aux/IAA genes, IAA 28 transcription is not induced by exogenous auxin.
Abstract: The phytohormone auxin is important in many aspects of plant development. We have isolated an auxin-resistant Arabidopsis mutant, iaa28-1, that is severely defective in lateral root formation and that has diminished adult size and decreased apical dominance. The iaa28-1 mutant is resistant to inhibition of root elongation by auxin, cytokinin, and ethylene, but it responds normally to other phytohormones. We identified the gene defective in the iaa28-1 mutant by using a map-based positional approach and found it to encode a previously uncharacterized member of the Aux/IAA gene family. IAA28 is preferentially expressed in roots and inflorescence stems, and in contrast to other Aux/IAA genes, IAA28 transcription is not induced by exogenous auxin. Studies of the gain-of-function iaa28-1 mutant suggest that IAA28 normally represses transcription, perhaps of genes that promote lateral root initiation in response to auxin signals.
362 citations
TL;DR: The molecular defect in pxa1 is identified using a map-based positional approach and Homology to ALD protein and other human and yeast peroxisomal transporters suggests that PXA1 imports coenzyme A esters of fatty acids and IBA into the peroxISome for beta-oxidation.
Abstract: Peroxisomes are important organelles in plant metabolism, containing all the enzymes required for fatty acid beta-oxidation. More than 20 proteins are required for peroxisomal biogenesis and maintenance. The Arabidopsis pxa1 mutant, originally isolated because it is resistant to the auxin indole-3-butyric acid (IBA), developmentally arrests when germinated without supplemental sucrose, suggesting defects in fatty acid beta-oxidation. Because IBA is converted to the more abundant auxin, indole-3-acetic acid (IAA), in a mechanism that parallels beta-oxidation, the mutant is likely to be IBA resistant because it cannot convert IBA to IAA. Adult pxa1 plants grow slowly compared with wild type, with smaller rosettes, fewer leaves, and shorter inflorescence stems, indicating that PXA1 is important throughout development. We identified the molecular defect in pxa1 using a map-based positional approach. PXA1 encodes a predicted peroxisomal ATP-binding cassette transporter that is 42% identical to the human adrenoleukodystrophy (ALD) protein, which is defective in patients with the demyelinating disorder X-linked ALD. Homology to ALD protein and other human and yeast peroxisomal transporters suggests that PXA1 imports coenzyme A esters of fatty acids and IBA into the peroxisome for beta-oxidation. The pxa1 mutant makes fewer lateral roots than wild type, both in response to IBA and without exogenous hormones, suggesting that the IAA derived from IBA during seedling development promotes lateral root formation.
331 citations
TL;DR: IAA obtained through de novo synthesis, conjugate hydrolysis, or IBA β-oxidation may have different functions in plant development, and possible roles for the IAA derived from the various pathways are discussed.
Abstract: The phytohormone auxin is important in virtually all aspects of plant growth and development, yet our understanding of auxin homeostasis is far from complete Plants use several mechanisms to control levels of the active auxin, indole-3-acetic acid (IAA) Plants can synthesize IAA both from tryptophan (Trp-dependent pathways) and from a Trp precursor but bypassing Trp (Trp-independent pathways) Despite progress in identifying enzymes in Trp-dependent IAA biosynthesis, no single IAA biosynthetic pathway is yet defined to the level that all of the relevant genes, enzymes, and intermediates are identified In addition to de novo synthesis, vascular plants can obtain IAA from the hydrolysis of IAA conjugates IAA can be conjugated to amino acids, sugars, and peptides; endogenous conjugates that are active in bioassays and hydrolyzed in plants are likely to be important free IAA sources Conjugation is also used to permanently inactivate excess IAA, and these conjugates may be distinct from the hydrolyzable conjugates The peroxisomal (3-oxidation of endogenous indole-3-butyric acid (IBA) also can supply plants with IAA, which may account for part of the auxin activity of exogenous IBA Compartmentalization of enzymes and precursors may contribute to the regulation of auxin metabolism IAA obtained through de novo synthesis, conjugate hydrolysis, or IBA β-oxidation may have different functions in plant development, and possible roles for the IAA derived from the various pathways are discussed
194 citations
TL;DR: The cloned CHY1, which appears to encode a peroxisomal protein 43% identical to a mammalian valine catabolic enzyme that hydrolyzes β-hydroxyisobutyryl-CoA, supports the hypothesis that the energy-intensive sequence unique toValine catabolism, where an intermediate CoA ester is hydrolyzed and a new CoAEster is formed two steps later, avoids methacrylyl- CoA accumulation.
100 citations
TL;DR: The results indicate that co-suppressing endogenous genes can cause dominant phenotypes as expected and it is predicted that this system will be generally useful for identifying genes that yield phenotypes upon over-expression as well.
Abstract: We have developed a system to over-express or co-suppress random cDNAs in Arabidopsis thaliana upon Agrobacterium tumefaciens-mediated transformation We constructed a binary vector containing a novel Arabidopsis cDNA library driven by the cauliflower mosaic virus (CaMV) 35S promoter The vector, 35SpBARN, offers in terra selection with glufosinate ammonium (BASTA) and the ability to identify the cDNA insert using PCR with flanking primers We introduced this overexpression library into Arabidopsis and selected over 30,000 transformants A random sample of 50 T1 plants was analyzed to determine the quality of the cDNA library in planta About 90% of T1 plants in the collection have inserts, the average insert size is ca 11 kb, and ca 43% of these inserts appear to encode full-length proteins T1 plants were screened for visible abnormalities, and one mutant, V5, was chosen for further study This mutant displays a pale green phenotype, and its transgene contains a partial petH cDNA encoding chloroplast ferredoxin-NADP+ reductase (EC 11812) This construct co-suppresses the endogenous petH transcript We recapitulated the mutant phenotype by expressing either the full-length or truncated petH cDNA from the CaMV 35S promoter in wild-type Arabidopsis Our results indicate that co-suppressing endogenous genes can cause dominant phenotypes as expected As we have also used the 35SpBARN vector to successfully over-express other transcripts in planta, we predict that this system will be generally useful for identifying genes that yield phenotypes upon over-expression as well
93 citations
TL;DR: Genetic and biochemical evidence indicates that auxin accelerates the degradation of the already short-lived Aux/IAA proteins to derepress transcription by ARF proteins.
70 citations