engleski

The tail of the TROL is necessary for efficinet photosynthesis

We used reverse genetics approach to identify novel thylakoid component, entitled TROL (thylakoid rhodanese-like), which is necessary for sustaining efficient photosynthetic electron transport under conditions of elevated light intensity. TROL combines rhodanese (thiosulfate sulfurtransferase)-like domain with a C-terminally possitioned repetitive module involved in binding of ferredoxin:NADP+ oxidoreductase (FNR). Localization studies using C-terminal YFP fusion confirmed chloroplast localization of TROL. In vitro chloroplast import assays established its thylakoid localization and demonstrated that TROL possesses characteristics of an integral membrane component. To confirm the assumption that TROL is involved in anchoring of FNR, the sequence module at the C-terminus of TROL was used as bait in two-hybrid screen using FNR gene as a target. Following yeast transformation, the expression of both protein products resulted in a number of colonies showing β -galactosidase activity. Furthermore, TROL was shown to co-immunoprecipitate with FNR. In transgenic Arabidopsis lines At4g01050 gene was inactivated by an insertion of a T-DNA element. Insertion leads to a complete depletion of TROL protein. We have also generated antisense lines in which TROL protein accumulation was lowered. Photosynthetic performance was investigated by Pulse-Amplitude fluorometry. Knock-out and antisense lines had severely lowered relative electron transport rate at light intensities exceeding 250 µ ; ; molPHOTONS m-2s-1. Simultaneously, the amount of nonphotochemical quenching increases, indicating enhanced dissipation of absorbed light energy as heat. We conclude that TROL represents a thylakoid membrane docking site for the assembly of a ternary complex between FNR, ferredoxin and NAD(P). Deletion of TROL leads to overreduction of thylakoids, indicating that formation of such an anchored complex is required for oriented interaction between electron donor and acceptor in order to accommodate their respective redox centres in optimal orientation for efficient electron transfer.

photosynthesis; chloroplasts; FNR; redox-regulation

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