Multiple Facets of Arabidopsis Seedling Development Require * Indole-3-Butyric Acid-Derived Auxin

Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005, USA.
The Plant Cell (Impact Factor: 9.34). 03/2011; 23(3):984-99. DOI: 10.1105/tpc.111.083071
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Levels of auxin, which regulates both cell division and cell elongation in plant development, are controlled by synthesis, inactivation, transport, and the use of storage forms. However, the specific contributions of various inputs to the active auxin pool are not well understood. One auxin precursor is indole-3-butyric acid (IBA), which undergoes peroxisomal β-oxidation to release free indole-3-acetic acid (IAA). We identified ENOYL-COA HYDRATASE2 (ECH2) as an enzyme required for IBA response. Combining the ech2 mutant with previously identified iba response mutants resulted in enhanced IBA resistance, diverse auxin-related developmental defects, decreased auxin-responsive reporter activity in both untreated and auxin-treated seedlings, and decreased free IAA levels. The decreased auxin levels and responsiveness, along with the associated developmental defects, uncover previously unappreciated roles for IBA-derived IAA during seedling development, establish IBA as an important auxin precursor, and suggest that IBA-to-IAA conversion contributes to the positive feedback that maintains root auxin levels.

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Available from: Rebekah A Rampey, Oct 02, 2015
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    • "However, this is not supported by an ech2 ibr1 ibr3 ibr10 quadruple mutant, which has severe defects in the conversion of IBA to IAA in peroxisomes. The quadruple mutant exhibits smaller cotyledons, slower leaf development, and delayed flowering, but it has no gross morphological defects at maturity and its inflorescences are fertile and appear similar to those of wild-type plants (Strader et al., 2011). The pale green leaves of kat2 kat5 plants were reminiscent of the reduced chlorophyll observed in the pex5- 10 mutant that lacks a full-length PEX5 protein (Khan and Zolman, 2010). "
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    ABSTRACT: A specific function for peroxisomal β-oxidation in inflorescence development in Arabidopsis thaliana is suggested by the mutation of the ABNORMAL INFLORESCENCE MERISTEM 1 gene, which encodes one of two peroxisomal multifunctional proteins. Therefore, it should be possible to identify other β-oxidation mutants that recapitulate the aim1 phenotype. Three genes encode peroxisomal 3-ketoacyl-CoA thiolase (KAT) in Arabidopsis. KAT2 and KAT5 are present throughout angiosperms whereas KAT1 is a Brassicaceae-specific duplication of KAT2 expressed at low levels in Arabidopsis. KAT2 plays a dominant role in all known aspects of peroxisomal β-oxidation, including that of fatty acids, pro-auxins, jasmonate precursor oxophytodienoic acid, and trans-cinnamic acid. The functions of KAT1 and KAT5 are unknown. Since KAT5 is conserved throughout vascular plants and expressed strongly in flowers, kat2 kat5 double mutants were generated. These were slow growing, had abnormally branched inflorescences, and ectopic organ growth. They made viable pollen, but produced no seed indicating that infertility was due to defective gynaecium function. These phenotypes are strikingly similar to those of aim1. KAT5 in the Brassicaceae encodes both cytosolic and peroxisomal proteins and kat2 kat5 defects could be complemented by the re-introduction of peroxisomal (but not cytosolic) KAT5. It is concluded that peroxisomal KAT2 and KAT5 have partially redundant functions and operate downstream of AIM1 to provide β-oxidation functions essential for inflorescence development and fertility.
    Journal of Experimental Botany 10/2014; 65(22). DOI:10.1093/jxb/eru397 · 5.53 Impact Factor
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    • "Accordingly, the present results demonstrate that auxin accumulated in the endodermis-derived cell clusters and meristemoids of the AR-forming IBA + Kin-cultured TCLs, with a PIN1 expression pattern parallel to that observed in planta. IBA is a natural precursor of IAA (Strader and Bartel, 2011), and an efficient IBA to IAA conversion is important for arabidopsis LR formation (Strader et al., 2011). It is possible that exogenous IBA is rapidly converted to IAA in the TCL cells close to the medium, and PIN1 directs IAA efflux to the endodermis, inducing in some cells of this tissue an IAA accumulation sufficient for AR initiation. "
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    ABSTRACT: Background and AimsAdventitious roots (ARs) are part of the root system in numerous plants, and are required for successful micropropagation. In the Arabidopsis thaliana primary root (PR) and lateral roots (LRs), the quiescent centre (QC) in the stem cell niche of the meristem controls apical growth with the involvement of auxin and cytokinin. In arabidopsis, ARs emerge in planta from the hypocotyl pericycle, and from different tissues in in vitro cultured explants, e.g. from the stem endodermis in thin cell layer (TCL) explants. The aim of this study was to investigate the establishment and maintenance of the QC in arabidopsis ARs, in planta and in TCL explants, because information about this process is still lacking, and it has potential use for biotechnological applications.Methods Expression of PR/LR QC markers and auxin influx (LAX3)/efflux (PIN1) genes was investigated in the presence/absence of exogenous auxin and cytokinin. Auxin was monitored by the DR5::GUS system and cytokinin by immunolocalization. The expression of the auxin-biosynthetic YUCCA6 gene was also investigated by in situ hybridization in planta and in AR-forming TCLs from the indole acetic acid (IAA)-overproducing superroot2-1 mutant and its wild type.Key ResultsThe accumulation of auxin and the expression of the QC marker WOX5 characterized the early derivatives of the AR founder cells, in planta and in in vitro cultured TCLs. By determination of PIN1 auxin efflux carrier and LAX3 auxin influx carrier activities, an auxin maximum was determined to occur at the AR tip, to which WOX5 expression was restricted, establishing the positioning of the QC. Cytokinin caused a restriction of LAX3 and PIN1 expression domains, and concomitantly the auxin biosynthesis YUCCA6 gene was expressed in the apex.Conclusions In ARs formed in planta and TCLs, the QC is established in a similar way, and auxin transport and biosynthesis are involved through cytokinin tuning.
    Annals of Botany 09/2013; 112(7). DOI:10.1093/aob/mct215 · 3.65 Impact Factor
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    • "Mutants with defects of peroxisomal biosynthesis or b-oxidation are resistant to externally applied IBA (Zolman et al., 2000, 2001a,b; Zolman & Bartel, 2004). Several mutants of peroxisomal enzymes appear to be solely linked to b-oxidation-like processing of IBA to IAA (Zolman et al., 2008; Strader et al., 2011). Moreover, mutants defective in b-oxidation are impaired in IBA to IAA conversion (Strader et al., 2010). "
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    ABSTRACT: Controlled plant growth requires regulation through a variety of signaling molecules, including steroids, peptides, radicals of oxygen and nitrogen, as well as the 'classical' phytohormone groups. Auxin is critical for the control of plant growth and also orchestrates many developmental processes, such as the formation of new roots. It modulates root architecture both slowly, through actions at the transcriptional level and, more rapidly, by mechanisms targeting primarily plasma membrane sensory systems and intracellular signaling pathways. The latter reactions use several second messengers, including Ca(2+) , nitric oxide (NO) and reactive oxygen species (ROS). Here, we investigated the different roles of two auxins, the major auxin indole-3-acetic acid (IAA) and another endogenous auxin indole-3-butyric acid (IBA), in the lateral root formation process of Arabidopsis and maize. This was mainly analyzed by different types of fluorescence microscopy and inhibitors of NO production. This study revealed that peroxisomal IBA to IAA conversion is followed by peroxisomal NO, which is important for IBA-induced lateral root formation. We conclude that peroxisomal NO emerges as a new player in auxin-induced root organogenesis. In particular, the spatially and temporally coordinated release of NO and IAA from peroxisomes is behind the strong promotion of lateral root formation via IBA.
    New Phytologist 06/2013; 200(2). DOI:10.1111/nph.12377 · 7.67 Impact Factor
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