Chlorophylls (Chls) are essential cofactors for photosynthesis. One of the least understood steps of Chl biosynthesis is formation of the fifth (E) ring, where the red substrate, magnesium protoporphyrin IX monomethyl ester, is converted to the green product, 3,8-divinyl protochlorophyllide a In oxygenic phototrophs, this reaction is catalyzed by an oxygen-dependent cyclase, consisting of a catalytic subunit (AcsF/CycI) and an auxiliary protein, Ycf54. Deletion of Ycf54 impairs cyclase activity and results in severe Chl deficiency, but its exact role is not clear. Here, we used a Δycf54 mutant of the model cyanobacterium Synechocystis sp. PCC 6803 to generate suppressor mutations that restore normal levels of Chl. Sequencing Δycf54 revertants identified a single D219G amino acid substitution in CycI and frameshifts in slr1916, which encodes a putative esterase. Introduction of these mutations to the original Δycf54 mutant validated the suppressor effect, especially in combination. However, comprehensive analysis of the Δycf54 suppressor strains revealed that the D219G-substituted CycI is only partially active and its accumulation is misregulated, suggesting that Ycf54 controls both the level and activity of CycI. We also show that Slr1916 has Chl dephytylase activity in vitro and its inactivation up-regulates the entire Chl biosynthetic pathway, resulting in improved cyclase activity. Finally, large-scale bioinformatic analysis indicates that our laboratory evolution of Ycf54-independent CycI mimics natural evolution of AcsF in low-light-adapted ecotypes of the oceanic cyanobacteria Prochlorococcus, which lack Ycf54, providing insight into the evolutionary history of the cyclase enzyme.

• Klíčová slova
• chlorophyll, cyanobacteria, cyclase, microevolution, photosynthesis,
• MeSH
• bakteriální proteiny genetika   metabolismus   MeSH
• bakteriochlorofyly biosyntéza   genetika   MeSH
• delece genu * MeSH
• oxygenasy genetika   metabolismus   MeSH
• Prochlorococcus genetika   metabolismus   MeSH
• Synechocystis genetika   metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• bakteriální proteiny MeSH
• bakteriochlorofyly MeSH
• oxygenasy MeSH

BACKGROUND AND AIMS: We have recently shown that an Arabidopsis thaliana double mutant of type III phosphatidylinositol-4-kinases (PI4Ks), pi4kβ1β2, constitutively accumulated a high level of salicylic acid (SA). By crossing this pi4kβ1β2 double mutant with mutants impaired in SA synthesis (such as sid2 impaired in isochorismate synthase) or transduction, we demonstrated that the high SA level was responsible for the dwarfism phenotype of the double mutant. Here we aimed to distinguish between the SA-dependent and SA-independent effects triggered by the deficiency in PI4Kβ1 and PI4Kβ2. METHODS: To achieve this we used the sid2pi4kβ1β2 triple mutant. High-throughput analyses of phytohormones were performed on this mutant together with pi4kβ1β2 and sid2 mutants and wild-type plants. Responses to pathogens, namely Hyaloperonospora arabidopsidis, Pseudomonas syringae and Botrytis cinerea, and also to the non-host fungus Blumeria graminis, were also determined. Callose accumulation was monitored in response to flagellin. KEY RESULTS: We show here the prominent role of high SA levels in influencing the concentration of many other tested phytohormones, including abscisic acid and its derivatives, the aspartate-conjugated form of indole-3-acetic acid and some cytokinins such as cis-zeatin. We show that the increased resistance of pi4kβ1β2 plants to the host pathogens H. arabidopsidis, P. syringae pv. tomato DC3000 and Bothrytis cinerea is dependent on accumulation of high SA levels. In contrast, accumulation of callose in pi4kβ1β2 after flagellin treatment was independent of SA. Concerning the response to Blumeria graminis, both callose accumulation and fungal penetration were enhanced in the pi4kβ1β2 double mutant compared to wild-type plants. Both of these processes occurred in an SA-independent manner. CONCLUSIONS: Our data extensively illustrate the influence of SA on other phytohormone levels. The sid2pi4kβ1β2 triple mutant revealed the role of PI4Kβ1/β2 per se, thus showing the importance of these enzymes in plant defence responses.

• Klíčová slova
• Arabidopsis thaliana, biotic stress, callose, isochorismate synthase 1, pathogens, phytohormones, pi4kβ1β2/PI4Ks, salicylic acid,
• MeSH
• 1-fosfatidylinositol-4-kinasa * MeSH
• Arabidopsis * MeSH
• kyselina salicylová MeSH
• mutace MeSH
• nemoci rostlin MeSH
• proteiny huseníčku genetika   MeSH
• Pseudomonas syringae MeSH
• regulace genové exprese u rostlin MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• 1-fosfatidylinositol-4-kinasa * MeSH
• AT5G09350 protein, Arabidopsis MeSH Prohlížeč
• AT5G64070 protein, Arabidopsis MeSH Prohlížeč
• kyselina salicylová MeSH
• proteiny huseníčku MeSH

Plants, like other multicellular organisms, survive through a delicate balance between growth and defense against pathogens. Salicylic acid (SA) is a major defense signal in plants, and the perception mechanism as well as downstream signaling activating the immune response are known. Here, we identify a parallel SA signaling that mediates growth attenuation. SA directly binds to A subunits of protein phosphatase 2A (PP2A), inhibiting activity of this complex. Among PP2A targets, the PIN2 auxin transporter is hyperphosphorylated in response to SA, leading to changed activity of this important growth regulator. Accordingly, auxin transport and auxin-mediated root development, including growth, gravitropic response, and lateral root organogenesis, are inhibited. This study reveals how SA, besides activating immunity, concomitantly attenuates growth through crosstalk with the auxin distribution network. Further analysis of this dual role of SA and characterization of additional SA-regulated PP2A targets will provide further insights into mechanisms maintaining a balance between growth and defense.

• Klíčová slova
• NPR1, PIN, PP2A, auxin, auxin transport, gravitropism, immunity, phosphorylation, protein phosphatase 2A, salicylic acid,
• MeSH
• Arabidopsis růst a vývoj   fyziologie   MeSH
• imunita rostlin MeSH
• kořeny rostlin růst a vývoj   metabolismus   MeSH
• kyselina salicylová metabolismus   MeSH
• kyseliny indoloctové metabolismus   MeSH
• proteinfosfatasa 2 metabolismus   MeSH
• proteiny huseníčku metabolismus   MeSH
• signální transdukce * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• kyselina salicylová MeSH
• kyseliny indoloctové MeSH
• PIN2 protein, Arabidopsis MeSH Prohlížeč
• PP2A protein, Arabidopsis MeSH Prohlížeč
• proteinfosfatasa 2 MeSH
• proteiny huseníčku MeSH