Large-scale chlorophyll (Chl) degradation,along with concomitant anthocyanin biosynthesis,creates the magnificent canopy scenery in the autumn.Dynamic Chl degradation greatly facilitates plant growth and development by remobilizing nutrients from senescing organs to rapidly developing ones,seeds and storage organs in particular.In the last decade or so,the major Chl degradation pathway,termed the pheophorbide a oxygenase (PAO) pathway,has been extensively characterized by identifying Chl catabolic genes (CCGs) or enzymes (CCEs).Chl a is the degradable form of Chls;while Chl b needs to be converted to Chl a before being channeled for degradation (Figure 1A).