Why E. coli? Have you thought about using something like Pichia pastoris that will better accommodate a membrane associated plant protein, while not sacrifice cell density in your cultures? While I don't know about membrane preps our lab has had a lot of success purifying fungal proteins from Pichia, and I know a significant amount of work has been done with functional expression of membrane-associated human P450s in Pichia.
I have tried expressing it in BL21, Lemo 21, RIL, C41, C43, But could not even get expression of it. I have also tried different IPTG conc. and different temp. but could not help...