Strigolactone plant hormones control plant architecture and are key players in both symbiotic and parasitic interactions. They contain an ABC tricyclic lactone connected to a butenolide group, the D-ring. The DWARF14 (D14) strigolactone receptor belongs to the superfamily of α/β-hydrolases and is known to hydrolyze the bond between the ABC lactone and the D-ring. Here we characterize the binding and catalytic functions of RAMOSUS3 (RMS3), the pea (Pisum sativum) ortholog of rice (Oryza sativa) D14 strigolactone receptor. Using novel profluorescent probes with strigolactone-like bioactivity, we show that RMS3 acts as a single-turnover enzyme that explains its apparent low enzymatic rate. We further demonstrate the formation of a covalent RMS3/D-ring complex, essential for bioactivity, in which the D-ring is attached to Histidine 247 of the catalytic triad. These results reveal an undescribed mechanism of plant hormone reception where the receptor performs an irreversible enzymatic reaction to generate its own ligand.

Plants are under relentless challenge by pathogenic bacteria, fungi, and oomycetes, for whom they provide a resource of living space and nutrients. Upon detection of pathogens, plants carry out multiple layers of defense response, orchestrated by a tightly organized network of hormones. In this review, we provide an overview of the phytohormones involved in immunity and the ways pathogens manipulate their biosynthesis and signaling pathways. We highlight recent developments, including the discovery of a defense signaling molecule, new insights into hormone biosynthesis, and the increasing importance of signaling hubs at which hormone pathways intersect.

Highlights d Physcomitrella patens provides an early evolutionary snapshot of 11 KAI2-like proteins d A loop segment determines substrate specificity in Physcomitrella KAI2-like proteins d Distinct groups of proteins perceive (À)-5-deoxystrigol and the karrikin KAR 1 d Physcomitrella KAI2-like proteins cannot complement Arabidopsis kai2 or d14 mutants

No abstract

Finding the target: activity-based proteomic profiling probes based on the depalmitoylation inhibitors palmostatin B and M have been synthesized and were found to target acyl protein thioesterase 1 (APT1) and 2 (APT2) in cells.

The ethylene response factor (ERF) transcription factors are integral components of environmental stress signaling cascades, regulating a wide variety of downstream genes related to stress responses and plant development. However, the mechanisms by which ERF genes regulate the heat stress response are not well understood. Here, we uncover the positive role of ethylene signaling, ERF95 and ERF97 in basal thermotolerance of Arabidopsis thaliana. We demonstrate that ethylene signaling-defective mutants exhibit compromised basal thermotolerance, whereas plants with constitutively activated ethylene response show enhanced basal thermotolerance. EIN3 physically binds to the promoters of ERF95 and ERF97. Ectopic constitutive expression of ERF95 or ERF97 increases the basal thermotolerance of plants. In contrast, erf95 erf96 erf97 erf98 quadruple mutants exhibit decreased basal thermotolerance. ERF95 and ERF97 genetically function downstream of EIN3. ERF95 can physically interact with ERF97, and this interaction is heat inducible. ERF95 and ERF97 regulate a common set of target genes, including known heat-responsive genes and directly bind to the promoter of HSFA2. Thus, our study reveals that the EIN3-ERF95/ERF97-HSFA2 transcriptional cascade may play an important role in the heat stress response, thereby establishing a connection between ethylene and its downstream regulation in basal thermotolerance of plants.

RPGR-interacting protein 1 (RPGRIP1) is mutated in the eye disease Leber congenital amaurosis (LCA) and its structural homolog, RPGRIP1-like (RPGRIP1L), is mutated in many different ciliopathies. Both are multidomain proteins that are predicted to interact with retinitis pigmentosa G-protein regulator (RPGR). RPGR is mutated in X-linked retinitis pigmentosa and is located in photoreceptors and primary cilia. We solved the crystal structure of the complex between the RPGR-interacting domain (RID) of RPGRIP1 and RPGR and demonstrate that RPGRIP1L binds to RPGR similarly. RPGRIP1 binding to RPGR affects the interaction with PDEδ, the cargo shuttling factor for prenylated ciliary proteins. RPGRIP1-RID is a C2 domain with a canonical β sandwich structure that does not bind Ca(2+) and/or phospholipids and thus constitutes a unique type of protein-protein interaction module. Judging from the large number of C2 domains in most of the ciliary transition zone proteins identified thus far, the structure presented here seems to constitute a cilia-specific module that is present in multiprotein transition zone complexes.

possess a catalytic triad consisting of a serine, an aspartate, and a histidine. The published crystal structure of APT1 (PDB ID 1fj2) showed that the protein has indeed a canonical ␣ / ␤ hydrolase fold and presented the protein in its dimeric form ( 2 ). The only other crystal structures known among the lysophospholipase family are carboxylesterase from two different bacteria (e.g., PDB ID 1auo, Fig. 1 includes the corresponding sequence labeled "CARB_H21.01_P_fl uorescens_1AUO") and two uncharacterized proteins (PDB ID 3b5e and 2r8b, SCOP database, Carboxylesterase/thioesterase 1 family) ( 3 ). APT1 is the best-characterized protein of the family and is known to depalmitoylate G ␣ -proteins as well as Ras proteins, and thus is involved in the modulation of the Ras signaling pathway that plays an important role in various types of cancer. The cellular localization of H-Ras and N-Ras is maintained by a palmitoylation/depalmitoylation cycle ( 4 ) that can be disturbed by APT1 inhibitors in vivo ( 5 ), leading to a reversal of the transforming effects induced by active Ras. The close relationship between the LYPLAL1 and APT1 families and the presence of the catalytic triad suggested a cellular function comparable to APT1. However, LYPLAL1 was also proposed to act as a triglyceride lipase in adipose tissue ( 6 ), and several studies indicated a signifi cant relationship between the lyplal1 gene locus and the waist-hip ratio of study participants ( 7, 8 ) as well as fat distribution ( 9 ) and nonalcoholic fatty liver disease ( 10 ). Yet, the biological function and signifi cance of LYPLAL1 remained barely investigated, because no structural or biochemical information was available, so we set out to solve the crystal structure of human LYPLAL1 and characterize its enzymatic properties.Abstract Sequence homology indicates the existence of three human cytosolic acyl protein thioesterases, including APT1 that is known to depalmitoylate H-and N-Ras. One of them is the lysophospholipase-like 1 (LYPLAL1) protein that on the one hand is predicted to be closely related to APT1 but on the other hand might also function as a potential triacylglycerol lipase involved in obesity. However, its role remained unclear. The 1.7 Å crystal structure of LYPLAL1 reveals a fold very similar to APT1, as expected, but features a shape of the active site that precludes binding of long-chain substrates. Biochemical data demonstrate that LYPLAL1 exhibits neither phospholipase nor triacylglycerol lipase activity, but rather accepts short-chain substrates. Furthermore, extensive screening efforts using chemical array technique revealed a fi rst small molecule inhibitor of LYPLAL1. The human acyl protein thioesterases APT1, APT2, and the protein lysophospholipase-like 1 (LYPLAL1) belong, according to their amino acid sequence identities, to two different subclasses of the lysophospholipase family ( Fig. 1 ), which is in turn a subclass of the ␣ / ␤ hydrolases superfamily ( 1 ). A BLAST search with LYPLAL1 fi nds acyl protein thioesterases as the ...