From chloroplast to membrane: the contributions of copper proteins in regulating leaf senescence

C. HAO, X. W. DENG, L. LI

State Key Laboratory of Protein and Plant Gene Research, School of Advanced Agricultural Sciences, Peking University, Beijing 100871, China

Leaf senescence is a critical process in plants and has a direct impact on many important agronomic traits. Despite decades of research on senescence-altered mutants and functional assessment of senescence-associated genes (SAGs), the original senescence signal and the molecular mechanism that perceives and transduces the signal remain elusive. Here, we show that copper is rapidly remobilized during senescence prior to the onset of senescence symptoms. By profiling the transcriptomes and tracking the subcellular copper distribution, we found that reciprocal copper allocation between plastocyanin, the key mobile electron carrier in the Z-scheme of photosynthetic electron transport, and SAG14 and plantacyanin (PCY), a pair of interacting small blue copper proteins located on the endomembrane, is a common thread in different leaf senescence scenarios. Phylogenetic analysis and genetic evidences suggest that plastocyanin, conserved in all the main Archaeplastida clades, have two homologous genes with different function in Arabidopsis and some other crops. Meanwhile, we also found that the pair of blue copper proteins may regulate copper allocation to the ethylene signaling pathway and control senescence by modulating ethylene sensitivity. Further deciphering the copper signaling should provide new insights into our understanding of the fundamental question of how plants age.