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Gene amplification followed by functional diversification is a major force in evolution. A typical example of this is seen in the WUSCHEL-RELATED HOMEOBOX ( WOX ) gene family, named after the Arabidopsis stem cell regulator WUSCHEL . Here we analyze functional divergence in the WOX gene family. Members of the WUS clade, except the cambium stem cell regulator WOX4 , can substitute for WUS function in shoot and floral stem cell maintenance to different degrees. Stem cell function of WUS requires a canonical WUS-box, essential for interaction with TPL/TPR co-repressors, whereas the repressive EAR domain is dispensable and the acidic domain seems only to be required for female fertility. In contrast to the WUS clade, members of the ancient WOX13 and the WOX9 clades cannot support stem cell maintenance. Although the homeodomains are interchangeable between WUS and WOX9 clade members, a WUS-compatible homeodomain together with canonical WUS-box is not sufficient for stem cell maintenance. Our results suggest that WOX function in shoot and floral meristems of Arabidopsis is restricted to the modern WUS clade, suggesting that stem cell control is a derived function. Yet undiscovered functional domains in addition to the homeodomain and the WUS-box are necessary for this function. [ABSTRACT FROM AUTHOR]

A letter is presented that proposes a rapid screening method for the parallel determination of various phytohormones such as abscisic acid (ABA) and indole-3-acetic acid (IAA), and phytoalexins like camalexin and scopoleptin in various plant species, notably "Arabidopsis thaliana" and "Nicotiana tabacum." It claims that this method can increase the process of physiological phenotyping in plants, thus helping researchers to develop effective strategies for the protection of agricultural crops.

Lateral roots are initiated postembryonically in response to environmental cues, enabling plants to explore efficiently their under-ground environment. However, the mechanisms by which the environment determines the position of lateral root formation are unknown. In this study, we demonstrate that in Arabidopsis thaliana lateral root initiation can be induced mechanically by either gravitropic curvature or by the transient bending of a root by hand. The plant hormone auxin accumulates at the site of lateral root induction before a primordium starts to form. Here we describe a subcellular relocalization of PIN1, an auxin transport protein, in a single protoxylem cell in response to gravitropic curvature. This relocalization precedes auxin-dependent gene transcription at the site of a new primordium. Auxin-dependent nuclear signaling is necessary for lateral root formation; arf7/19 double knock-out mutants normally form no lateral roots but do so upon bending when the root tip is removed. Signaling through arf7/19 can therefore be bypassed by root bending. These data support a model in which a root-tip-derived signal acts on down- stream signaling molecules that specify lateral root identity. [ABSTRACT FROM AUTHOR]

A comparative transcriptome analysis for successive stages of Arabidopsis (Arabidopsis thaliana) developmental leaf senescence (NS), darkening-induced senescence of individual leaves attached to the plant (DIS), and senescence in dark-incubated detached leaves (DET) revealed many novel senescence-associated genes with distinct expression profiles. The three senescence processes share a high number of regulated genes, although the overall number of regulated genes during DIS and DET is about 2 times lower than during NS. Consequently, the number of NS-specific genes is much higher than the number of DIS- or DET-specific genes. The expression profiles of transporters (TPs), receptor-like kinases, autophagy genes, and hormone pathways were analyzed in detail. The Arabidopsis TPs and other integral membrane proteins were systematically reclassified based on the Transporter Classification system. Coordinate activation or inactivation of several genes is observed in some TP families in all three or only in individual senescence types, indicating differences in the genetic programs for remobilization of catabolites. Characteristic senescence type-specific differences were also apparent in the expression profiles of (putative) signaling kinases. For eight hormones, the expression of biosynthesis, metabolism, signaling, and (partially) response genes was investigated. In most pathways, novel senescence-associated genes were identified. The expression profiles of hormone homeostasis and signaling genes reveal additional players in the senescence regulatory network. [ABSTRACT FROM AUTHOR]

Transgenic Arabidopsis thaliana plants harboring the Agrobacterium tumefaciens phytohormone-biosynthetic genes iaaM and iaaH display an altered development indicative of elevated auxin levels. These plants exhibit an increased apical dominance, increased hypocotyl and petiole length and epinastic leaves and cotyledons. In addition, the transgenic plants display the formation of necrotic spots on leaves and bracts in soil and an altered behavior of axillary buds in tissue culture. Despite transcriptional activity of the iaaM and iaaH promoters in the vasculature of root tissue, root development of young iaaM/iaaH transgenic plants is identical to wild type. However, transgenic iaaM/iaaH plants grown under tissue culture conditions for a prolonged period display both vigorous and ectopic root growth. The level of free IAA in the rosette of the iaaM/iaaH transgenic plants is increased approximately 2-fold compared to wild type. The number of cells comprising the vascular tissue in hypocotyls and inflorescence stems of the transgenic plants is reduced and these plants exhibit a reduced basipetal polar auxin transport in the inflorescence stems. This reduced polar auxin transport probably accounts for the rapid auxin effect on the aerial part of the transgenic plants and the late effect on root development. [ABSTRACT FROM AUTHOR]

The complex dominant Arabidopsis thaliana mutant lettuce (let) shows the conversion of the leaf petiole into a leaf blade caused by an ectopic leaf blade formation. This is the result of the activation tagging of the LEAFY PETIOLE (LEP) gene encoding an AP2/EREBP-like transcription factor. Here, we report that in addition to this leafy petiole phenotype, the size of the vascular bundles is increased in all aerial organs in letas a result of an increase in the number of xylem, phloem (pro)cambial and pericycle cells. This vascular phenotype is caused by activation tagging of the two genes VASCULAR TISSUE SIZE (VAS) and LEP. These genes are closely linked and arranged in tandem. Activation tagging of LEP only caused a specific increase in the number of xylem cells. This increased xylem cell number, together with the ectopic leaf blade formation, indicates that LEP functions as a cell division-promoting factor. The activation tagging of VAS only resulted in a specific increase in phloem (pro)cambial and pericycle cells. We conclude that activation tagging of LEP and VAS results in additive phenotypes. Insertional mutants for LEP and VAS display wildtype vascular development, indicating the relevance of activation tagging for functional analysis of novel genes involved in plant development. [ABSTRACT FROM AUTHOR]

The Arabidopsis thaliana (L.) Heynh. mutant delayed-dehiscence2-2 (dde2-2) was identified in an En1/Spm1 transposon-induced mutant population screened for plants showing defects in fertility. The dde2-2 mutant allele is defective in the anther dehiscence process and filament elongation and thus exhibits a male-sterile phenotype. The dde2-2 phenotype can be rescued by application of methyl jasmonate, indicating that the mutant is affected in jasmonic acid biosynthesis. The combination of genetic mapping and a candidate-gene approach identified a frameshift mutation in the ALLENE OXIDE SYNTHASE (AOS) gene, encoding one of the key enzymes of jasmonic acid biosynthesis. Expression analysis and genetic complementation of the dde2-2 phenotype by overexpression of the AOS coding sequence confirmed that the male-sterile phenotype is indeed caused by the mutation in the AOS gene. [ABSTRACT FROM AUTHOR]

Summary The Arabidopsis thaliana tpt-1 mutant which is defective in the chloroplast triose phosphate/phosphate translocator (TPT) was isolated by reverse genetics. It contains a T-DNA insertion 24 bp upstream of the start ATG of the TPT gene. The mutant lacks TPT transcripts and triose phosphate (TP)-specific transport activities are reduced to below 5% of the wild type. Analyses of diurnal variations in the contents of starch, soluble sugars and phosphorylated intermediates combined with 14 CO2 labelling studies showed, that the lack of TP export for cytosolic sucrose biosynthesis was almost fully compensated by both continuous accelerated starch turnover and export of neutral sugars from the stroma throughout the day. The utilisation of glucose 6-phosphate (generated from exported glucose) rather than TP for sucrose biosynthesis in the light bypasses the key regulatory step catalysed by cytosolic fructose 1,6-bisphosphatase. Despite its regulatory role in the feed-forward control of sucrose biosynthesis, variations in the fructose 2,6-bisphosphate content upon illumination were similar in the mutant and the wild type. Crosses of tpt-1 with mutants unable to mobilise starch (sex1 ) or to synthesise starch (adg1-1 ) revealed that growth and photosynthesis of the double mutants was severely impaired only when starch biosynthesis, but not its mobilisation, was affected. For tpt-1 /sex1 combining a lack in the TPT with a deficiency in starch mobilisation, an additional compensatory mechanism emerged, i.e. the formation and (most likely) fast turnover of high molecular weight polysaccharides. Steady-state RNA levels and transport activities of other phosphate translocators capable of transporting TP remained unaffected in the mutants. [ABSTRACT FROM AUTHOR]

Summary Stem cells in plants and animals are maintained pluripotent by signals from adjacent niche cells. In plants, WUSCHEL HOMEOBOX (WOX) transcription factors are central regulators of stem cell maintenance in different meristem types, yet their molecular mode of action has remained elusive. Here we show that in the Arabidopsis root meristem, the WOX5 protein moves from the root niche organizer, the quiescent center, into the columella stem cells, where it directly represses the transcription factor gene CDF4 . This creates a gradient of CDF4 transcription, which promotes differentiation opposite to the WOX5 gradient, allowing stem cell daughter cells to exit the stem cell state. We further show that WOX5 represses CDF4 transcription by recruiting TPL/TPR co-repressors and the histone deacetylase HDA19, which consequently induces histone deacetylation at the CDF4 regulatory region. Our results show that chromatin-mediated repression of differentiation programs is a common strategy in plant and animal stem cell niches. [ABSTRACT FROM AUTHOR]

Plant genomes contain a large number of genes encoding for berberine bridge enzyme (BBE)-like enzymes. Despite the widespread occurrence and abundance of this protein family in the plant kingdom, the biochemical function remains largely unexplored. In this study, we have expressed two members of the BBE-like enzyme family from Arabidopsis thaliana in the host organism Komagataella pastoris. The two proteins, termed AtBBE-like 13 and AtBBE-like 15, were purified, and their catalytic properties were determined. In addition, AtBBE-like 15 was crystallized and structurally characterized by x-ray crystallography. Here, we show that the enzymes catalyze the oxidation of aromatic allylic alcohols, such as coumaryl, sinapyl, and coniferyl alcohol, to the corresponding aldehydes and that AtBBE-like 15 adopts the same fold as vanillyl alcohol oxidase as reported previously for berberine bridge enzyme and other FAD-dependent oxidoreductases. Further analysis of the substrate range identified coniferin, the glycosylated storage form of coniferyl alcohol, as a substrate of the enzymes, whereas other glycosylated monolignols were rather poor substrates. A detailed analysis of the motifs present in the active sites of the BBE-like enzymes in A. thaliana suggested that 14 out of 28 members of the family might catalyze similar reactions. Based on these findings, we propose a novel role of BBE-like enzymes in monolignol metabolism that was previously not recognized for this enzyme family. [ABSTRACT FROM AUTHOR]