LSU family members and NBR1 are novel factors that contribute to homeostasis of catalases and peroxisomes in Arabidopsis thaliana

The short coiled-coil LSU (RESPONSE TO LOW SULFUR) proteins are linked to sulfur metabolism and have numerous protein partners. However, most of these partners lack direct links to sulfur metabolism, and the role of such interactions remains elusive. Here, we confirmed LSU binding to Arabidopsis catalase (CAT) and revealed that NBR1, a selective autophagy receptor, strongly interacts with LSU1 but not with CAT. Consequently, we observed the involvement of autophagy but not NBR1 in CAT removal. The lsu and nbr1 mutants differed from the wild-type plants in size and the number of yellow fluorescent protein (YFP)-CAT condensates, the number of peroxisomes, and photosynthetic pigments levels in the presence and absence of stress. We conclude that LSU family members and NBR1 contribute directly or indirectly to CAT and peroxisome homeostasis, and the overall fitness of plants. Our structural models of CAT-LSU complexes show at least two regions of interaction in CAT, one of which is at the N-terminus. Indeed, the N-terminally truncated variants of CAT2 and CAT3 interact more weakly with LSU1 than their full-length variants, but the extent of reduction is higher for CAT2, suggesting differences in recognition of CAT2 and CAT3 by LSU1.