Unveiling the Molecular Mechanisms of Plant Autophagy-From Autophagosomes to Vacuoles in Plants.

Autophagy is an evolutionarily conserved intracellular vacuolar process. Since Christian de Duve first coined the term 'autophagy' in 1963, it had not been well understood at the molecular level until much later, due to limitations in biochemical approaches and/or morphological approaches posed by electron microscopy. An important milestone was achieved with the isolation and identification of autophagy-related (ATG) genes by genetic screening using yeast Saccharomyces cerevisiae. ATG genes are well conserved in most eukaryotic organisms, which allowed the subsequent isolation of ATG gene-knockouts in plants. From the phenotypic analyses of the autophagy-defective plants, the physiological roles of autophagy have been predicted. However, in some cases, all the phenotypes cannot be simply explained by defects in autophagy. Therefore, in order to fully understand the physiological implications of plant autophagy, it is quite important to elucidate the molecular mechanisms involved in each process in macro-/micro-autophagy. Although, until recently, our understanding of the molecular mechanisms of plant autophagy was lagging compared to similar research in yeast and animals, current studies have made many great advances in the plant research field. In this review, we discuss current knowledge of the molecular mechanisms of plant autophagy, from autophagy-induction/autophagosome-formation to vacuolar degradation, comparing these to processes in yeast and mammals. We also review aspects of plant autophagy research that require further investigation in the future.