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Plants optimize their growth and survival through highly integrated regulatory networks that coordinate defensive measures and developmental transitions in response to environmental cues. Protein phosphatase 2A (PP2A) is a key signaling component that controls stress reactions and growth at different stages of plant development, and the PP2A regulatory subunit PP2A-B'γ is required for negative regulation of pathogenesis responses and for maintenance of cell homeostasis in short-day conditions. Here, we report molecular mechanisms by which PP2A-B'γ regulates Botrytis cinerea resistance and leaf senescence in Arabidopsis ( Arabidopsis thaliana ). We extend the molecular functionality of PP2A-B'γ to a protein kinase-phosphatase interaction with the defense-associated calcium-dependent protein kinase CPK1 and present indications this interaction may function to control CPK1 activity. In presenescent leaf tissues, PP2A-B'γ is also required to negatively control the expression of salicylic acid-related defense genes, which have recently proven vital in plant resistance to necrotrophic fungal pathogens. In addition, we find the premature leaf yellowing of pp2a - b'γ depends on salicylic acid biosynthesis via SALICYLIC ACID INDUCTION DEFICIENT2 and bears the hallmarks of developmental leaf senescence. We propose PP2A-B'γ age-dependently controls salicylic acid-related signaling in plant immunity and developmental leaf senescence., (© 2020 American Society of Plant Biologists. All Rights Reserved.)

Nitrogen dioxide (NO 2 ) forms in plants under stress conditions, but little is known about its physiological functions. Here, we explored the physiological functions of NO 2 in plant cells using short-term fumigation of Arabidopsis ( Arabidopsis thaliana ) for 1 h with 10 µL L -1 NO 2. Although leaf symptoms were absent, the expression of genes related to pathogen resistance was induced. Fumigated plants developed basal disease resistance, or pattern-triggered immunity, against the necrotrophic fungus Botrytis cinerea and the hemibiotrophic bacterium Pseudomonas syringae Functional salicylic acid and jasmonic acid (JA) signaling pathways were both required for the full expression of NO 2 -induced resistance against B. cinerea An early peak of salicylic acid accumulation immediately after NO 2 exposure was followed by a transient accumulation of oxophytodienoic acid. The simultaneous NO 2 -induced expression of genes involved in jasmonate biosynthesis and jasmonate catabolism resulted in the complete suppression of JA and JA-isoleucine (JA-Ile) accumulation, which was accompanied by a rise in the levels of their catabolic intermediates 12-OH-JA, 12-OH-JA-Ile, and 12-COOH-JA-Ile. NO 2 -treated plants emitted the volatile monoterpene α-pinene and the sesquiterpene longifolene (syn. junipene), which could function in signaling or direct defense against pathogens. NO 2 -triggered B. cinerea resistance was dependent on enhanced early callose deposition and CYTOCHROME P450 79B2 ( CYP79B2 ), CYP79B3 , and PHYTOALEXIN DEFICIENT3 gene functions but independent of camalexin, CYP81F2 , and 4-OH-indol-3-ylmethylglucosinolate derivatives. In sum, exogenous NO 2 triggers basal pathogen resistance, pointing to a possible role for endogenous NO 2 in defense signaling. Additionally, this study revealed the involvement of jasmonate catabolism and volatiles in pathogen immunity., (© 2018 American Society of Plant Biologists. All rights reserved.)

In Arabidopsis (Arabidopsis thaliana), a number of defense-related metabolites are synthesized via indole-3-acetonitrile (IAN), including camalexin and indole-3-carboxylic acid (ICOOH) derivatives. Cytochrome P450 71A13 (CYP71A13) is a key enzyme for camalexin biosynthesis and catalyzes the conversion of indole-3-acetaldoxime (IAOx) to IAN. The CYP71A13 gene is located in tandem with its close homolog CYP71A12, also encoding an IAOx dehydratase. However, for CYP71A12, indole-3-carbaldehyde and cyanide were identified as major reaction products. To clarify CYP71A12 function in vivo and to better understand IAN metabolism, we generated two cyp71a12 cyp71a13 double knockout mutant lines. CYP71A12-specific transcription activator-like effector nucleases were introduced into the cyp71a13 background, and very efficient somatic mutagenesis was achieved. We observed stable transmission of the cyp71a12 mutation to the following generations, which is a major challenge for targeted mutagenesis in Arabidopsis. In contrast to cyp71a13 plants, in which camalexin accumulation is partially reduced, double mutants synthesized only traces of camalexin, demonstrating that CYP71A12 contributes to camalexin biosynthesis in leaf tissue. A major role of CYP71A12 was identified for the inducible biosynthesis of ICOOH. Specifically, the ICOOH methyl ester was reduced to 12% of the wild-type level in AgNO3-challenged cyp71a12 leaves. In contrast, indole-3-carbaldehyde derivatives apparently are synthesized via alternative pathways, such as the degradation of indole glucosinolates. Based on these results, we present a model for this surprisingly complex metabolic network with multiple IAN sources and channeling of IAOx-derived IAN into camalexin biosynthesis. In conclusion, transcription activator-like effector nuclease-mediated mutation is a powerful tool for functional analysis of tandem genes in secondary metabolism., (© 2015 American Society of Plant Biologists. All Rights Reserved.)

Indolic secondary metabolites play an important role in pathogen defense in cruciferous plants. In Arabidopsis (Arabidopsis thaliana), in addition to the characteristic phytoalexin camalexin, derivatives of indole-3-carbaldehyde (ICHO) and indole-3-carboxylic acid (ICOOH) are synthesized from tryptophan via the intermediates indole-3-acetaldoxime and indole-3-acetonitrile. Based on feeding experiments combined with nontargeted metabolite profiling, their composition in nontreated and silver nitrate (AgNO 3 )-treated leaf tissue was comprehensively analyzed. As major derivatives, glucose conjugates of 5-hydroxyindole-3-carbaldehyde, ICOOH, and 6-hydroxyindole-3-carboxylic acid were identified. Quantification of ICHO and ICOOH derivative pools after glucosidase treatment revealed that, in response to AgNO 3 treatment, their total accumulation level was similar to that of camalexin. ARABIDOPSIS ALDEHYDE OXIDASE1 (AAO1), initially discussed to be involved in the biosynthesis of indole-3-acetic acid, and Cytochrome P450 (CYP) 71B6 were found to be transcriptionally coexpressed with camalexin biosynthetic genes. CYP71B6 was expressed in Saccharomyces cerevisiae and shown to efficiently convert indole-3-acetonitrile into ICHO and ICOOH, thereby releasing cyanide. To evaluate the role of both enzymes in the biosynthesis of ICHO and ICOOH derivatives, knockout and overexpression lines for CYP71B6 and AAO1 were established and analyzed for indolic metabolites. The observed metabolic phenotypes suggest that AAO1 functions in the oxidation of ICHO to ICOOH in both nontreated and AgNO 3 -treated leaves, whereas CYP71B6 is relevant for ICOOH derivative biosynthesis specifically after induction. In summary, a model for the biosynthesis of ICHO and ICOOH derivatives is presented., (© 2014 American Society of Plant Biologists. All Rights Reserved.)