Auxin plays an essential role in many aspects of plant growth and development, including embryogenesis, vascular formation, apical dominance and tropism. Indole-3-acetic acid (IAA) is the most important naturally occurring auxin, but IAA biosynthesis in plants has been unclear for more than 70 years. Recently, the main IAA biosynthesis pathway was identified by molecular genetic and biochemical approaches. The TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA) family and the YUCCA (YUC) flavin monooxygenase family produce IAA from tryptophan by the two-step conversion in Arabidopsis. This article reviews the recent progress on auxin biosynthesis and its regulation in plants.

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Indole 3-acetic acid (IAA), predominant naturally occurring auxin plays a central role in plant growth and development. This small hormonal molecule regulates diverse developmental processes throughout the plant life. Auxin action is regulated by three major steps ; metabolism, transport and signaling. These highly complicated pathway and redundant functional proteins often hinder the genetic approach. To compliment genetic tools, small molecule probes have been widely utilized to elucidate auxin pathways. Here, we give an overview of small molecule probes used in auxin research and the chemical biology approaches to auxin biology.

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Phototropism allows plants to change their growth direction in response to the location of the light source. Asymmetric distribution of the phytohormone auxin occurs in response to a phototropic stimulus, and causes differential growth on the two sides of the plant organ and consequent organ bending. Recently, molecular genetic analyses of Arabidopsis have begun to shed light on the molecular mechanisms underlying this response system, including phototropin blue light photoreceptors, phototropin signaling components, auxin transporters and others. This review highlights some of the recent progress on the control of auxin transport in the phototropic response.

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Lateral root (LR) formation is one of the auxin-mediated developmental processes in vascular plants. Physiological and genetic studies using Arabidopsis thaliana and other plant species have revealed the role of auxin biosynthesis, transport and signaling in LR initiation and primordium development. These studies have shown that auxin-regulated transcription through Auxin/Indole-3-Acetic Acid (Aux/IAA) and AUXIN RESPONSE FACTOR (ARF) protein families is important for the developmental steps during LR formation : 1) the IAA28-ARFs module regulates LR founder cell specification, 2) the SOLITARY-ROOT(SLR)/IAA14-ARF7-ARF19 module regulates nuclear migration and asymmetric cell divisions of the LR founder cells for LR initiation, 3) the BODENLOS/IAA12-MONOPTEROS/ARF5 module also regulates LR initiation and organogenesis, and 4) the SHY2/IAA3-ARFs module regulates LR primordium development and LR emergence. This review summarizes recent findings on auxin-mediated LR formation, focusing on the molecular mechanisms of SLR/IAA14-ARF7-ARF19 module-dependent LR initiation.

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Certain plant lineages increase their environmental fitness by producing specialized metabolites via acquisition of novel enzyme functions. Flavonoids are major secondary metabolites widespread in land plants, and are most commonly conjugated with various sugar moieties by UDPsugar dependent glycosyltransferases (UGT) in a lineage-specific manner. For instant, flavonoid glucuronosyltransferases responsible for specialized metabolites (flavonoid glucuronide) in distinct plant lineages; e.g. perilla, daisy, and grapevine have differentiated independently from each parental glucosyltransferase by acquisition of different Arg residue required for their sugar donor specificity changes. Thus, the plasticity of sugar donor specificity of UGT explains, in part, the extraordinary structural diversification of phytochemicals observed in nature.

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Inflorescence characterized by clusters of florets, rather than simple flowers, is often used as cut flowers. The number of florets and the shape of inflorescence have a significant impact on the quality and price of cut flowers, and therefore, controlling these characters is crucial in cut flower production. The mechanism of inflorescence architecture development appears to intricately change depending on the hereditary factors and cultivation conditions, but it has some regularity, too. In this paper, it is explained that the mechanism of inflorescence architecture development for the purpose of stable production of cut flowers, especially of Gypsophila paniculata using a term of "regularity" as a keyword.

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Herbicides inhibiting very-long-chain fatty acid elongases (VLCFAEs), which catalyze the biosynthesis of very-long-chain fatty acids in plants, are categorized in the group K3 by the US Herbicide Resistance Action Committee (HRAC). This group includes many classes of herbicide, namely chloroacetamide, oxyacetamide, tetrazolinone, triazole and oxirane. Metolachlor and acetochlor are representatives of the chloroacetamide herbicide. Flufenacet and mefenacet are oxyacetamide herbicides. Fentrazamide is a tetrazolinone herbicide. Cafenstrole is a triazole herbicide. Indanofan is an oxirane herbicide. Pyroxasulfone for use in upland crops and fenoxasulfone for use in rice are isoxazoline-type herbicides which have new chemical structures. These two herbicides potently inhibit VLCFAEs. Sulfoxide and sulfone of a thiocarbamate herbicide, benthiocarb, which is categorized in the group N by the HRAC, also inhibits VLCFAEs. All classes of these VLCFAE-inhibiting herbicides reversibly inhibit the VLCFAE. This inhibition manner proposes a new inhibition mechanism of the VLCFAE, which is different from the commonly accepted hypothesis that VLCFAE-inhibiting herbicides irreversibly react with VLCFAEs as the chloroacetamidetype herbicides do.

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