There is abundant evidence of multiple biosynthesis pathways for the major naturally occurring auxin in plants, indole-3-acetic acid (IAA), and examples of differential use of two general routes of ...IAA synthesis, namely Trp-dependent and Trp-independent. Although none of these pathways has been completely defined, we now have examples of specific IAA biosynthetic pathways playing a role in developmental processes by way of localized IAA synthesis, causing us to rethink the interactions between IAA synthesis, transport, and signaling. Recent work also points to some IAA biosynthesis pathways being specific to families within the plant kingdom, whereas others appear to be more ubiquitous. An important advance within the past 5 years is our ability to monitor IAA biosynthesis and metabolism at increasingly higher resolution.
Summary
Collections of micro‐organisms are a crucial element of life science research infrastructure but are vulnerable to loss and damage caused by natural or man‐made disasters, the untimely death ...or retirement of personnel, or the loss of research funding. Preservation of biological collections has risen in priority due to a new appreciation for discoveries linked to preserved specimens, emerging hurdles to international collecting and decreased funding for new collecting. While many historic collections have been lost, several have been preserved, some with dramatic rescue stories. Rescued microbes have been used for discoveries in areas of health, biotechnology and basic life science. Suggestions for long‐term planning for microbial stocks are listed, as well as inducements for long‐term preservation.
Polar transport of the plant hormone auxin controls many aspects of plant growth and development. A number of synthetic compounds have been shown to block the process of auxin transport by inhibition ...of the auxin efflux carrier complex. These synthetic auxin transport inhibitors may act by mimicking endogenous molecules. Flavonoids, a class of secondary plant metabolic compounds, have been suggested to be auxin transport inhibitors based on their in vitro activity. The hypothesis that flavonoids regulate auxin transport in vivo was tested in Arabidopsis by comparing wild-type (WT) and transparent testa (tt4) plants with a mutation in the gene encoding the first enzyme in flavonoid biosynthesis, chalcone synthase. In a comparison between tt4 and WT plants, phenotypic differences were observed, including three times as many secondary inflorescence stems, reduced plant height, decreased stem diameter, and increased secondary root development. Growth of WT Arabidopsis plants on naringenin, a biosynthetic precursor to those flavonoids with auxin transport inhibitor activity in vitro, leads to a reduction in root growth and gravitropism, similar to the effects of synthetic auxin transport inhibitors. Analyses of auxin transport in the inflorescence and hypocotyl of independent tt4 alleles indicate that auxin transport is elevated in plants with a tt4 mutation. In hypocotyls of tt4, this elevated transport is reversed when flavonoids are synthesized by growth of plants on the flavonoid precursor, naringenin. These results are consistent with a role for flavonoids as endogenous regulators of auxin transport.
We used tryptophan auxotrophs of the dicot Arabidopsis thaliana (wall cress) to determine whether tryptophan has the capacity to serve as a precursor to the auxin, indole-3-acetic acid (IAA). ...Quantitative gas chromatography-selected ion monitoring-mass spectrometry (GC-SIM-MS) revealed that the trp2-1 mutant, which is defective in the conversion of indole to tryptophan, accumulated amide- and ester-linked IAA at levels 38-fold and 19-fold, respectively, above those of the wild type. Tryptophan and free IAA were isolated from the trp2-1 mutant grown in the presence of 15Nanthranilate and 2H5tryptophan, and the relative N and 2H5 enrichments of tryptophan and IAA were determined via GC-SIM-MS. The N enrichment of tryptophan, 13% +/- 4%, was less than the 15N enrichment of the IAA pool, 39% +/- 4%; therefore, IAA biosynthesis occurs via a tryptophan independent pathway. The amount of 2H5 incorporated by the plant into IAA from tryptophan (9% +/- 4%) was low and only slightly above the level of spontaneous, nonenzymatic conversion of 2H5tryptophan to 2H5IAA. These results show that the dicot Arabidopsis is similar to the monocot Zea mays in that the major route of IAA biosynthesis does not occur through tryptophan.
Indole-3-acetonitrile (IAN) is a candidate precursor of the plant growth hormone indole-3-acetic acid (IAA). We demonstrated that IAN has auxinlike effects on Arabidopsis seedlings and that exogenous ...IAN is converted to IAA in vivo. We isolated mutants with reduced sensitivity to IAN that remained sensitive to IAA. These mutants were recessive and fell into a single complementation group that mapped to chromosome 3, within 0.5 centimorgans of a cluster of three nitrilase-encoding genes, NIT1, NIT2, and NIT3. Each of the three mutants contained a single base change in the coding region of the NIT1 gene, and the expression pattern of NIT1 is consistent with the IAN insensitivity observed in the nit1 mutant alleles. The half-life of IAN and levels of IAA and IAN were unchanged in the nit1 mutant, confirming that Arabidopsis has other functional nitrilases. Overexpressing NIT2 in transgenic Arabidopsis caused increased sensitivity to IAN and faster turnover of exogenous IAN in vivo
Rethinking auxin biosynthesis and metabolism Normanly, J. (University of Massachusetts, Amherst, MA.); Slovin, J.P; Cohen, J.D
Plant physiology (Bethesda),
02/1995, Letnik:
107, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Charles Darwin cited the 1871 Ph.D. thesis of Theophil Ciesielski when he postulated in 1880 that a "transmitted influence" present in the tip of plant shoots was responsible for gravitropism. Both ...Darwin and Ciesielski had realized that the influence was affecting growth differentially. This influence was given the name auxin more than 50 years later and subsequently any compound that promoted growth in specific bioassays was defined as an auxin. The chemical structure of the primary plant auxin, IAA (Fig. 1), has been known since the 1930s to be a 3-substituted indole like Trp. Since that time, the prevailing theory has been that IAA is derived from Trp. However, due to lack of convincing evidence, the biosynthetic pathway for IAA in plants is still undefined. Within the last 10 years, development of precise quantitative methods, good model systems for in vivo analysis, and mutants altered in IAA metabolism have resulted in substantial progress in our understanding of IAA biosynthesis. This review focuses on the new and more complex picture of IAA biosynthesis that has emerged as a result of recent experiments
The plant hormone auxin regulates many aspects of plant growth and development. Although several auxin biosynthetic pathways have been proposed, none of these pathways has been precisely defined at ...the molecular level. Here we provide in planta evidence that the two Arabidopsis cytochrome P450s, CYP79B2 and CYP79B3, which convert tryptophan (Trp) to indole-3-acetaldoxime (IAOx) in vitro, are critical enzymes in auxin biosynthesis in vivo. IAOx is thus implicated as an important intermediate in auxin biosynthesis. Plants overexpressing CYP79B2 contain elevated levels of free auxin and display auxin overproduction phenotypes. Conversely, cyp79B2 cyp79B3 double mutants have reduced levels of IAA and show growth defects consistent with partial auxin deficiency. Together with previous work on YUCCA, a flavin monooxygenase also implicated in IAOx production, and nitrilases that convert indole-3-acetonitrile to auxin, this work provides a framework for further dissecting auxin biosynthetic pathways and their regulation.
Plants derive a number of important secondary metabolites from the amino acid tryptophan (Trp), including the growth regulator indole-3-acetic acid (IAA) and defense compounds against pathogens and ...herbivores. In previous work, we found that a dominant overexpression allele of the Arabidopsis (Arabidopsis thaliana) Myb transcription factor ATR1, atr1D, activates expression of a Trp synthesis gene as well as the Trp-metabolizing genes CYP79B2, CYP79B3, and CYP83B1, which encode enzymes implicated in production of IAA and indolic glucosinolate (IG) antiherbivore compounds. Here, we show that ATR1 overexpression confers elevated levels of IAA and IGs. In addition, we show that an atr1 loss-of-function mutation impairs expression of IG synthesis genes and confers reduced IG levels. Furthermore, the atr1-defective mutation suppresses Trp gene dysregulation in a cyp83B1 mutant background. Together, this work implicates ATR1 as a key homeostatic regulator of Trp metabolism and suggests that ATR1 can be manipulated to coordinately control the suite of enzymes that synthesize IGs.
Auxin metabolism encompasses transport, conjugation, deconjugation, conversion, and catabolism. The balance between auxin metabolism and biosynthesis determines the actual level of the hormone in a ...given cell and consequently plays an important role in many developmental processes from seed germination to fruit ripening. Mass spectrometry used in conjunction with stable isotope labeling studies has enabled comprehensive examination of auxin biosynthesis and turnover along with the identification of many auxin conjugate. It appears that the conjugate moiety may signal the metabolic fate (e.g. storage and eventual hydrolysis to free hormone, or catabolism). Recently identified auxin‐metabolizing enzymes are encoded by gene families which vary in specificity for auxin metabolites. The expression patterns of these genes will reveal a great deal about the mechanics of auxin metabolism.
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