Interfering RNA was used to suppress the expression of the genes At1g06680 and At2g30790 in Arabidopsis thaliana, which encode the PsbP‐1 and PsbP‐2 proteins, respectively, of Photosystem II. A phenotypic series of transgenic plants was recovered that expressed intermediate and low amounts of PsbP. Earlier we had documented significant alterations in a variety of Photosystem II parameters in these plant lines [Yi, X., Liu, H., Hargett, S. R., Frankel, L. K., Bricker, T. M. (2007). The PsbP protein is required for photosystem II complex assembly/stability and photoautotrophy in Arabidopsis thaliana. J. Biol. Chem. 34, 24833–24841]. In this communication, we document extensive defects in the thylakoid membrane architecture of these plants. Interestingly, strong interfering RNA suppression of the genes encoding the PsbQ protein (At4g21280 and At4g05180) was found to have no effect on the architecture of thylakoid membranes.