PGR5 is a small chloroplast protein that performs cyclic electron flow (CEF) around photosystem I and it is required for the proton gradient generation across the thylakoid membrane. The level of this protein is closely regulated by PGRL1. However, the molecular mechanism of PGR5 is still elusive. In this work, we have generated a new pgr5 mutant in Arabidopsis using CRISPR-Cas9 technology, pgr5-Cas, completely devoid of PGR5. We performed comparative proteomic analysis on pgr5-1 and pgr5-Cas lines (#1 and #2), as well as on pgrl1ab mutant.