Leaf senescence, as the last stage of leaf development, is regulated by diverse developmental and environmental factors. Jasmonates (JAs) have been shown to induce leaf senescence in several plant species; however, the molecular mechanism for JA-induced leaf senescence remains unknown. In this study, proteomic, genetic, and physiological approaches were used to reveal the molecular basis of JA-induced leaf senescence in Arabidopsis (Arabidopsis thaliana). We identified 35 coronatineinsensitive 1 (COI1)-dependent JA-regulated proteins using two-dimensional difference gel electrophoresis in Arabidopsis. Among these 35 proteins, Rubisco activase (RCA) was a COI1-dependent JA-repressed protein. We found that RCA was downregulated at the levels of transcript and protein abundance by JA in a COI1-dependent manner. We further found that loss of RCA led to typical senescence-associated features and that the COI1-dependent JA repression of RCA played an important role in JA-induced leaf senescence.

Mutations in , which encodes leucine-rich repeat kinase 2, are the most common genetic cause of familial and sporadic Parkinson's disease (PD), a degenerative disease of the central nervous system that causes impaired motor function and, in advanced stages, dementia. Dementia is a common symptom of another neurodegenerative disease, Alzheimer's disease, and research suggests that there may be pathophysiological and genetic links between the two diseases. Aggregates of β amyloid [a protein produced through cleavage of amyloid precursor protein (APP)] are seen in both diseases and in PD patients carrying G2019S-mutant LRRK2. Using patient-derived cells, brain tissue, and PD model mice, we found that LRRK2 interacted with and phosphorylated APP at Thr within its intracellular domain (AICD). Phosphorylation of APP at Thr promoted AICD transcriptional activity and correlated with increased nuclear abundance of AICD and decreased abundance of a dopaminergic neuron marker in cultures and brain tissue. The AICD regulates the transcription of genes involved in cytoskeletal dynamics and apoptosis. Overexpression of AICD, but not a phosphodeficient mutant (AICD), increased the loss of dopaminergic neurons in older mice expressing LRRK2 Moreover, the amount of Thr-phosphorylated APP was substantially greater in postmortem brain tissue and dopaminergic neurons (generated by reprogramming skin cells) from LRRK2 patients than in those from healthy individuals. LRRK2 inhibitors reduced the phosphorylation of APP at Thr in the patient-derived dopaminergic neurons and in the midbrains of LRRK2 mice. Thus, APP is a substrate of LRRK2, and its phosphorylation promotes AICD function and neurotoxicity in PD.