TY - JOUR ID - 1279 TI - Complex regulation of the TIR/AFB family of auxin receptors JO - Proc Natl Acad Sci USA PY - 2009 SP - 22540-22545 AU - Parry, G. AU - Calderón Villalobos, L.I. AU - Prigge, M. AU - Peret, B. AU - Dharmasiri, S. AU - Itoh, H. AU - Lechner, E. AU - Gray, W.M. AU - Bennett, M. AU - Estelle, M. VL - 106(52) UR - http://www.pnas.org/content/106/52/22528.full DO - 10.1073/pnas.0911967106 AB - Auxin regulates most aspects of plant growth and development. The hormone is perceived by the TIR1/AFB family of F-box proteins acting in concert with the Aux/IAA transcriptional repressors. Arabidopsis plants that lack members of the TIR1/AFB family are auxin resistant and display a variety of growth defects. However, little is known about the functional differences between individual members of the family. Phylogenetic studies reveal that the TIR1/AFB proteins are conserved across land plant lineages and fall into four clades. Three of these subgroups emerged before separation of angiosperms and gymnosperms whereas the last emerged before the monocot-eudicot split. This evolutionary history suggests that the members of each clade have distinct functions. To explore this possibility in Arabidopsis, we have analyzed a range of mutant genotypes, generated promoter swap transgenic lines, and performed in vitro binding assays between individual TIR1/AFB and Aux/IAA proteins. Our results indicate that the TIR1/AFB proteins have distinct biochemical activities and that TIR1 and AFB2 are the dominant auxin receptors in the seedling root. Further, we demonstrate that TIR1, AFB2, and AFB3, but not AFB1 exhibit significant posttranscriptional regulation. The microRNA miR393 is expressed in a pattern complementary to that of the auxin receptors and appears to regulate TIR1/AFB expression. However our data suggest that this regulation is complex. Our results suggest that differences between members of the auxin receptor family may contribute to the complexity of auxin response. A2 - C1 - Molecular Signal Processing ER - TY - JOUR ID - 1043 TI - Jasmonates act with salicylic acid to confer basal thermotolerance in Arabidopsis thaliana JO - New Phytol PY - 2009 SP - 175-187 AU - Clarke, S.M. AU - Cristescu, S.M. AU - Miersch, O. AU - Harren, F.J.M. AU - Wasternack, C. AU - Mur, L.A.J. VL - 182 UR - http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2008.02735.x/abstract DO - 10.1111/j.1469-8137.2008.02735.x AB - The cpr5-1 Arabidopsis thaliana mutant exhibits constitutive activation of salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) signalling pathways and displays enhanced tolerance of heat stress (HS). cpr5-1 crossed with jar1-1 (a JA-amino acid synthetase) was compromised in basal thermotolerance, as were the mutants opr3 (mutated in OPDA reductase3) and coi1-1 (affected in an E3 ubiquitin ligase F-box; a key JA-signalling component). In addition, heating wild-type Arabidopsis led to the accumulation of a range of jasmonates: JA, 12-oxophytodienoic acid (OPDA) and a JA-isoleucine (JA-Ile) conjugate. Exogenous application of methyl jasmonate protected wild-type Arabidopsis from HS. Ethylene was rapidly produced during HS, with levels being modulated by both JA and SA. By contrast, the ethylene mutant ein2-1 conferred greater thermotolerance. These data suggest that JA acts with SA, conferring basal thermotolerance while ET may act to promote cell death. A2 - C1 - Molecular Signal Processing ER - TY - JOUR ID - 1079 TI - Disruption of Adenosine-5'-Phosphosulfate Kinase in Arabidopsis Reduces Levels of Sulfated Secondary Metabolites JO - Plant Cell PY - 2009 SP - 910-927 AU - Mugford, S.G. AU - Yoshimoto, N. AU - Reichelt, M. AU - Wirtz, M. AU - Hill, L. AU - Mugford, S.T. AU - Nakazato, Y. AU - Noji, M. AU - Takahashi, H. AU - Kramell, R. AU - Gigolashvili, T. AU - Flügge, U.-I. AU - Wasternack, C. AU - Gershenzon, J. AU - Hell, R. AU - Saito, K. AU - Kopriva, S. VL - 21 UR - DO - 10.1105/tpc.109.065581 AB - Plants can metabolize sulfate by two pathways, which branch at the level of adenosine 59-phosphosulfate (APS). APS can be reduced to sulfide and incorporated into Cys in the primary sulfate assimilation pathway or phosphorylated by APS kinase to 39-phosphoadenosine 59-phosphosulfate, which is the activated sulfate form for sulfation reactions. To assess to what extent APS kinase regulates accumulation of sulfated compounds, we analyzed the corresponding gene family in Arabidopsis thaliana. Analysis of T-DNA insertion knockout lines for each of the four isoforms did not reveal any phenotypical alterations. However, when all six combinations of double mutants were compared, the apk1 apk2 plants were significantly smaller than wild-type plants. The levels of glucosinolates, a major class of sulfated secondary metabolites, and the sulfated 12-hydroxyjasmonate were reduced approximately fivefold in apk1 apk2 plants. Although auxin levels were increased in the apk1 apk2 mutants, as is the case for most plants with compromised glucosinolate synthesis, typical high auxin phenotypes were not observed. The reduction in glucosinolates resulted in increased transcript levels for genes involved in glucosinolate biosynthesis and accumulation of desulfated precursors. It also led to great alterations in sulfur metabolism: the levels of sulfate and thiols increased in the apk1 apk2 plants. The data indicate that the APK1 and APK2 isoforms of APS kinase play a major role in the synthesis of secondary sulfated metabolites and are required for normalgrowth rates. A2 - C1 - Molecular Signal Processing ER - TY - JOUR ID - 1113 TI - Arabidopsis IAR4 modulates auxin response by regulating auxin homeostasis JO - Plant Physiol PY - 2009 SP - 748-758 AU - Quint, M. AU - Barkawi, L.S. AU - Fan, K.T. AU - Cohen, J.D. AU - Gray, W.M. VL - 150 UR - DO - 10.1104/pp.109.136671 AB - In a screen for enhancers of tir1-1 auxin resistance, we identified two novel alleles of the putative mitochondrial pyruvate dehydrogenase E1α-subunit, IAA-Alanine Resistant4 (IAR4). In addition to enhancing the auxin response defects of tir1-1, iar4 single mutants exhibit numerous auxin-related phenotypes including auxin-resistant root growth and reduced lateral root development, as well as defects in primary root growth, root hair initiation, and root hair elongation. Remarkably, all of these iar4 mutant phenotypes were rescued when endogenous indole-3-acetic acid (IAA) levels were increased by growth at high temperature or overexpression of the YUCCA1 IAA biosynthetic enzyme, suggesting that iar4 mutations may alter IAA homeostasis rather than auxin response. Consistent with this possibility, iar4 mutants exhibit increased Aux/IAA stability compared to wild type under basal conditions, but not in response to an auxin treatment. Measurements of free IAA levels detected no significant difference between iar4-3 and wild-type controls. However, we consistently observed significantly higher levels of IAA-amino acid conjugates in the iar4-3 mutant. Furthermore, using stable isotope-labeled IAA precursors, we observed a significant increase in the relative utilization of the Trp-independent IAA biosynthetic pathway in iar4-3. We therefore suggest that the auxin phenotypes of iar4 mutants are the result of altered IAA homeostasis. A2 - C1 - Molecular Signal Processing ER -