Adaptation to Fe-deficiency requires remodeling of the photosynthetic apparatus

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Abstract
The molecular mechanisms underlying the onset of Fe‐deficiency chlorosis and the maintenance of photosynthetic function in chlorotic chloroplasts are relevant to global photosynthetic productivity. We describe a series of graded responses of the photosynthetic apparatus to Fe‐deficiency, including a novel response that occurs prior to the onset of chlorosis, namely the disconnection of the LHCI antenna from photosystem I (PSI). We propose that disconnection is mediated by a change in the physical properties of PSI‐K in PSI in response to a change in plastid Fe content, which is sensed through the occupancy, and hence activity, of the Fe‐containing active site in Crd1. We show further that progression of the response involves remodeling of the antenna complexes—specific degradation of existing proteins coupled to the synthesis of new ones, and establishment of a new steady state with decreased stoichiometry of electron transfer complexes. We suggest that these responses are typical of a dynamic photosynthetic apparatus where photosynthetic function is optimized and photooxidative damage is minimized in graduated responses to a combination of nutrients, light quantity and quality.

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