Diversity in subcellular targeting of the PP2A B′η subfamily members

Abstract

Protein phosphatase 2A (PP2A) is a serine/threonine-specific phosphatase comprising a catalytic subunit (C), a scaffolding subunit (A), and a regulatory subunit (B). The B subunits are believed to be responsible for substrate specificity and localization of the PP2A complex. In plants, three families of B subunits exist, i.e. B (B55), B', and B''. Here, we report differential subcellular targeting within the Arabidopsis B'eta subfamily, which consists of the close homologs B'eta, B'theta, B'gamma and B'zeta. Phenotypes of corresponding knockouts were observed, and particularly revealed delayed flowering for the B'eta knockout. The B' subunits were linked to fluorescent tags and transiently expressed in various tissues of onion, tobacco and Arabidopsis. B'eta and B'gamma targeted the cytosol and nucleus. B'zeta localized to the cytoplasm and partly co-localized with mitochondrial markers when the N-terminus was free. Provided its C-terminus was free, the B'theta subunit targeted peroxisomes. The importance of the C-terminal end for peroxisomal targeting was further confirmed by truncation of the C-terminus. The results revealed that the closely related B' subunits are targeting different organelles in plants, and exemplify the usage of the peptide serine-serine-leucine as a PTS1 peroxisomal signaling peptide.

Protein phosphatase 2A regulatory subunits affecting plant innate immunity, energy metabolism, and flowering time – joint functions among B'η subfamily members

“…19 Moreover, 2 T-DNA insertion lines of B'h showed a delay in flowering. 7 In this study, b'u mutant plants showed a figure), B'z in mitochondria, and B'u in peroxisomes. 7 All members of the B'h subfamily are implicated in negative regulation of innate immunity.…”

“…7 In this study, b'u mutant plants showed a figure), B'z in mitochondria, and B'u in peroxisomes. 7 All members of the B'h subfamily are implicated in negative regulation of innate immunity. B'u is importing a PP2A holoenzyme into peroxisomes by piggybacking and is involved in energy metabolism.…”

“…In our recent studies we identified the PP2A-B'u holoenzyme to be located in peroxisomes and positively affecting peroxisomal b-oxidation, which apparently had consequences for hypocotyls growth. 17 To investigate if the other subfamily members would be involved in similar processes, T-DNA insertion lines for B'z, 7 and B'h 7 were analyzed by a sugar independence assay. Interestingly, seedlings of the b'z mutant showed hypocotyl retardation in both an 8 h light/16 h dark regimen ( Fig.…”

“…7 B'h was reported to be in nucleus and nucleolus, B'g in nucleus and cytosol, B'z in mitochondria, and B'u in the peroxisomes. 7 The physiological functions of these subunits are discussed here.…”

“…The sequence homology conservation is mostly located in the core region and comprises the distinct domains that are responsible for the interaction with the AC heterodimer. [6][7][8] Subcellular targeting of members of the h subfamily has been investigated using transient expression of fluorescent tagged proteins in isolated protoplasts and leaf tissue. 7 B'h was reported to be in nucleus and nucleolus, B'g in nucleus and cytosol, B'z in mitochondria, and B'u in the peroxisomes.…”