Fig. 4.

Iberis amara cucurbitadienol synthase is expressed in all plant organs tested and is a monotopic membrane protein. (A) Relative expression of IaCPQ in different I. amara organs quantified by qPCR. (B–R) Representative confocal images of the epidermal cell space ([B], [C], [F], [G], [J], [K], [O], [P]) and the nucleus ([D], [E], [H], [I], [M], [N], [Q], [R]) of Nicotiana benthamiana leaves expressing C-terminally tagged proteins. mRFP1 and CYP98A1 (P450) are used as controls for cytosolic and ER localization, respectively. Soluble mRFP1 is found in the nucleus and fills in gaps between plant cell compartments. ER-localized proteins (CpCPQ and CYP98A1) are restrained to nuclear membranes and a well-defined ER membrane network. IaCPQ is observed on the nuclear membrane as a monotopic membrane protein, however, excess protein appears to permeate the nucleus. Similar images were obtained with N-terminal fluorescent fusion constructs for IaCPQ and CpCPQ (supplementary fig. 6B, Supplementary Material online). Scale bars=10 µm.