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Plants evolve nucleotide-binding leucine-rich repeat receptors (NLRs) to induce immunity. Activated coiled-coil (CC) domain containing NLRs (CNLs) oligomerize and form apparent cation channels promoting calcium influx and cell death, with the alpha-1 helix of the individual CC domains penetrating the plasma membranes. Some CNLs are characterized by putative N-myristoylation and S-acylation sites in their CC domain, potentially mediating permanent membrane association. Whether activated Potentially Membrane Localized NLRs (PMLs) mediate cell death and calcium influx in a similar way is unknown. We uncovered the cell-death function at the vacuole of an atypical but conserved Arabidopsis PML, PML5, which has a significant deletion in its CC G10/GA domain. Active PML5 oligomers localize in Golgi membranes and the tonoplast, alter vacuolar morphology, and induce cell death, with the short N-terminus being sufficient. Mutant analysis supports a potential role of PMLs in plant immunity. PML5-like deletions are found in several Brassicales paralogs, pointing to the evolutionary importance of this innovation. PML5, with its minimal CC domain, represents the first identified CNL utilizing vacuolar-stored calcium for cell death induction., (© 2024. The Author(s).)

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is the major catalyst in the conversion of carbon dioxide into organic compounds in photosynthetic organisms. However, its activity is impaired by binding of inhibitory sugars such as xylulose-1,5-bisphosphate (XuBP), which must be detached from the active sites by Rubisco activase. Here, we show that loss of two phosphatases in Arabidopsis thaliana has detrimental effects on plant growth and photosynthesis and that this effect could be reversed by introducing the XuBP phosphatase from Rhodobacter sphaeroides. Biochemical analyses revealed that the plant enzymes specifically dephosphorylate XuBP, thus allowing xylulose-5-phosphate to enter the Calvin-Benson-Bassham cycle. Our findings demonstrate the physiological importance of an ancient metabolite damage-repair system in degradation of by-products of Rubisco, and will impact efforts to optimize carbon fixation in photosynthetic organisms., (© 2023. The Author(s).)