Challenges of in vivo protein localization in plants seen through the DEK1 protein lens

During the last 25 y, fluorescent protein tagging has become a tool of choice to investigate protein function in a cellular context. The information gathered with this approach is not only providing insights into protein subcellular localization but also allows contextualizing protein function in multicellular settings. Here we illustrate the power of this method by commenting on the recent successful localization of the large membrane DEK1 protein during three-dimensional body formation in the moss Physcomitrella patens. But as many approaches, protein tagging is not exempt of caveats. The multiple infructuous (failed) attempts to detect DEK1 using a fluorescent protein tag present a good overview of such potential problems. Here we discuss the insertion of different fluorescent proteins at different positions in the PpDEK1 protein and the resulting unintended range of mutant phenotypes. Albeit none of these mutants generated a detectable fluorescent signal they can still provide interesting biological information about DEK1 function.