Use your knowledge of the sulfur mobilization SUF pathway in

Use your knowledge of the sulfur mobilization (SUF) pathway in plastids (stroma), the involvement of NFU2 and NFU3 proteins in this pathway, the type of Fe-S clusters found in Photosystem I core proteins, to explain why the loss-of-function nfu2 and nfu3 mutants have a lower Photosystem I activity than the wild type plants? (References: Touraine et al. [2004] Plant Journal 40: 101-111; Yabe et al. (2004) Plant Cell 16: 993-1007; Nath et al. [2016] Plant Physiology 172, 2459-2470)

Solution

The presences of metalloproteins such as iron-sulfur (Fe-S) proteins are essential for the sulfur mobilization during ptohosystem I and for iron-independent flavin reductase system for electron donation (Fdr-Fdx). The plastidial involvement of NFU3 and NFU3 proteins are mainly associated with chlorophyll catabolism and sulfur mobilization so that these proteins are referred as “scaffold” proteins essential for, sulfur and nitrogen assimilation . In case mutant NF2 AND NFU3, these Fe-S iron centers may lead to lower “photosyntehsis activity” compared to wild-type plants finally result in low cellular iron regulation and lowered photo system I mediated sulfur and nitrogen assimilation