Essential protein for photoautotrophism. Confers resistance to photo-oxidative damages by contributing to the thermal dissipation of light energy and to lumenal acidification (increase of pH gradient). Component of the cytochrome b6-f complex, which mediates electron transfer between photosystem II (PSII) and photosystem I (PSI), cyclic electron flow around PSI, and state transitions (By similarity). a plastoquinol + 2 H(+)(in) + 2 oxidized [plastocyanin] = a plastoquinone + 4 H(+)(out) + 2 reduced [plastocyanin] Binds 1 [2Fe-2S] cluster per subunit. The 4 large subunits of the cytochrome b6-f complex are cytochrome b6, subunit IV (17 kDa polypeptide, petD), cytochrome f and the Rieske protein, while the 4 small subunits are petG, petL, petM and petN. The complex functions as a dimer (By similarity). Interacts with PGRL1A. The transmembrane helix obliquely spans the membrane in one monomer, and its extrinsic C-terminal domain is part of the other monomer. Confined to photosynthetic tissues, with highest levels in flowers. In leaves, mostly localized in mesophyll cells. In stems, confined to the peripheral ring of chlorenchyma and adjoining groups of cells associated with the vascular bundles. In siliques, present in green wall of the fruit and in peduncle but not in the translucide white septum of the seeds. Light-dependent expression. Inhibited by acidification of thylakoids (below pH 5), sucrose and norflurazon (caroteonid synthesis inhibitor leading to photobleaching). This protein is 1 of 2 subunits of the cytochrome b6-f complex that are encoded in the nucleus. The Rieske iron-sulfur protein is a high potential 2Fe-2S protein. May be due to an intron retention. Belongs to the Rieske iron-sulfur protein family.