The chloroplast clpP gene, encoding a proteolytic subunit of ATP-dependentprotease, is indispensable for chloroplast development in tobacco

ClpP is a proteolytic subunit of the ATP-dependent Clp protease, which is f ound in chloroplasts in higher plants. Proteolytic subunits are encoded bot h by the chloroplast gene, clpP, and a nuclear multi gene family. We insert ionally disrupted clpP by chloroplast transformation in tobacco. However, c omplete segregation was impossible, indicating that the chloroplast-encoded clpP gene has an indispensable function for cell survival, In the heteropl asmic clpP disruptant, the leaf surface was rough by clumping, and the late ral leaf expansion was irregularly arrested, which led to an asymmetric, sl ender leaf shape, Chloroplasts consisted of two populations: chloroplasts t hat were similar to the wild type, and small chloroplasts that emitted high chi fluorescence. Ultrastructural analysis of chloroplast development sugg ested that clpP disruption also induced swelling of the thylakoid lumen in the meristem plastids and inhibition of etioplast development in the dark. Tn mature leaves, thylakoid membranes of the smaller chloroplast population consisted exclusively of large stacks of tightly appressed membranes. Thes e results indicate that chloroplast-encoded ClpP is involved in multiple pr ocesses of chloroplast development, including a housekeeping function that is indispensable for cell survival.