Light-matter interactions as an emerging aspect of quantum optics enable exceptional physical phenomena and advanced applications in nanophotonics through the nanoscale exploitation of photon-emitter interactions. In this talk, we introduce cathodoluminescence (CL) microscopy to detect chiroptical effects in chiral plasmonic nanostructures, as guided by the reciprocity between electron beam and plane wave excitation, and we further realize the reveal and control of chiral cathodoluminescence at subnanoscale. Besides, CL microscopy can provide better physical insight of chiroptical effects and find new chiroptical phenomena that is obscured in the near field of the nanostructure and hardly detected by far-field optical characterization methods. Moreover, chiral radiative LDOS distributions in plasmonic nanostructures can be imaged at the nanoscale by using CL nanoscopy, which directly reflect the chiral radiative spontaneous decay of quantum emitters.