Caleosin/Peroxygenases: multifunctional proteins in plants

BACKGROUND: Caleosin/peroxygenases (CLO/PXGs) are a family of multifunctional proteins that are ubiquitous in land plants and also found in some fungi and green algae. CLO/PXGs were initially described as a class of plant lipid-associated proteins with some similarities to the oleosins that stabilize lipid droplets (LDs) in storage tissues such as seeds. However, we now know that CLO/PXGs have more complex structure, distribution and functions than oleosins. Structurally, CLO/PXGs share conserved domains that confer specific biochemical features with diverse localizations and functions.

SCOPE: This review surveys the structural properties of CLO/PXGs and their biochemical roles. In addition to their highly conserved structures, CLO/PXGs have peroxygenase activities and are involved in several aspects of oxylipin metabolism in plants. The enzymatic activities and the spatiotemporal expression of CLO/PXGs are described and linked with their wider involvement in plant physiology. Plant CLO/PXGs have many roles in both biotic and abiotic stress responses in plants and in their responses to environmental toxins. Finally, some intriguing developments in the biotechnological uses of CLO/PXGs are addressed.

CONCLUSIONS: It is now two decades since caleosin/peroxygenases (CLO/PXGs) were first recognized as a new class of lipid-associated proteins, and only 15 years since their additional enzymatic functions as a novel class of peroxygenases was discovered. There are many interesting research questions that remain to be addressed in future physiological studies of plant CLO/PXGs and also their recently discovered roles in the sequestration and possibly detoxification of a wide variety of lipidic xenobiotics that can challenge plant welfare.