Publikationen - Molekulare Signalverarbeitung

Plants adjust the balance between growth and defence using photoreceptors and jasmonates. Levels of active jasmonates are reduced in a phytochrome B-dependent manner by upregulation of a 12-hydroxyjasmonate sulfotransferase, leading to increase in shade avoidance and decrease in defence.

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Jasmonic acid biosynthesis starts in chloroplasts and is finalized in peroxisomes. The required export of a crucial intermediate out of the chloroplast is now shown to be mediated by a protein from the outer envelope called JASSY.

Jasmonic acid (JA) signaling can be switched off by metabolism of JA. The master regulator MYC2, interacting with MED25, has been shown to be deactivated by the bHLH transcription factors MTB1, MTB2, and MTB3. An autoregulatory negative feedback loop has been proposed for this termination in JA signaling.

Electric signaling and Ca2+ waves were discussed to occur in systemic wound responses. Two new overlapping scenarios were identified: (i) membrane depolarization in two special cell types followed by an increase in systemic cytoplasmic Ca2+ concentration ([Ca2+]cyt), and (ii) glutamate sensed by GLUTAMATE RECEPTOR LIKE proteins and followed by Ca2+-based defense in distal leaves.

Jasmonates (JAs) are signals in plant stress responses and development. One of the first observed and prominent responses to JAs is the induction of biosynthesis of different groups of secondary compounds. Among them are nicotine, isoquinolines, glucosinolates, anthocyanins, benzophenanthridine alkaloids, artemisinin, and terpenoid indole alkaloids (TIAs), such as vinblastine. This brief review describes modes of action of JAs in the biosynthesis of anthocyanins, nicotine, TIAs, glucosinolates and artemisinin. After introducing JA biosynthesis, the central role of the SCFCOI1-JAZ co-receptor complex in JA perception and MYB-type and MYC-type transcription factors is described. Brief comments are provided on primary metabolites as precursors of secondary compounds. Pathways for the biosynthesis of anthocyanin, nicotine, TIAs, glucosinolates and artemisinin are described with an emphasis on JA-dependent transcription factors, which activate or repress the expression of essential genes encoding enzymes in the biosynthesis of these secondary compounds. Applied aspects are discussed using the biotechnological formation of artemisinin as an example of JA-induced biosynthesis of secondary compounds in plant cell factories.

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For the first time a member of the CYP74 enzyme subfamily (9‐AOS) from tomato has been shown by chemical and analytical approaches to catalyze multiple reactions. These multifunctional properties of 9‐AOS from the oxylipin‐forming lipoxygenase (LOX) pathway raise several new questions on lipid‐derived signaling.

The allene oxide cyclase (AOC) catalyzes the formation of cis-(+)-12-oxophytodienoic acid, an intermediate in jasmonate biosynthesis and is encoded by a single copy gene in tomato. The full length AOC promoter isolated by genome walk contains 3600 bp. Transgenic tomato lines carrying a 1000 bp promoter fragment and the full length promoter, respectively, in front of the β-glucuronidase (GUS)-encoding uidA gene and several tobacco lines carrying the full length tomato AOC promoter before GUS were used to record organ- and tissue-specific promoter activities during development and in response to various stimuli. High promoter activities corresponding to immunocytochemically detected occurrence of the AOC protein were found in seeds and young seedlings and were confined to the root tip, hypocotyl and cotyledons of 3-d-old seedlings. In 10-d-old seedlings promoter activity appeared preferentially in the elongation zone. Fully developed tomato leaves were free of AOC promoter activity, but showed high activity upon wounding locally and systemically or upon treatment with JA, systemin or glucose. Tomato flowers showed high AOC promoter activities in ovules, sepals, anthers and pollen. Most of the promoter activity patterns found in tomato with the 1000 bp promoter fragment were also detected with the full length tomato AOC promoter in tobacco during development or in response to various stimuli. The data support a spatial and temporal regulation of JA biosynthesis during development and in response to environmental stimuli.

Several mammalian peptide hormones and proteins from plant and animal origin contain an N-terminal pyroglutamic acid (pGlu) residue. Frequently, the moiety is important in exerting biological function in either mediating interaction with receptors or stabilizing against N-terminal degradation. Glutaminyl cyclases (QCs) were isolated from different plants and animals catalyzing pGlu formation. The recent resolution of the 3D structures of Carica papaya and human QCs clearly supports different evolutionary origins of the proteins, which is also reflected by different enzymatic mechanisms. The broad substrate specificity is revealed by the heterogeneity of physiological substrates of plant and animal QCs, including cytokines, matrix proteins and pathogenesis-related proteins. Moreover, recent evidence also suggests human QC as a catalyst of pGlu formation at the N-terminus of amyloid peptides, which contribute to Alzheimer's disease. Obviously, owing to its biophysical properties, the function of pGlu in plant and animal proteins is very similar in terms of stabilizing or mediating protein and peptide structure. It is possible that the requirement for catalysis of pGlu formation under physiological conditions may have triggered separate evolution of QCs in plants and animals.