Macroautophagy occurs in distal TMV-uninfected root tip tissue of tomato taking place systemic PCD

Autophagy is an important mechanism for recycling cell materials upon encountering stress conditions. Our previous studies had shown that TMV infection could lead to systemic PCD in the distal uninfected tissues, including root tip and shoot tip tissues. But it is not clear whether there is autophagy in the distal apical meristem of TMV-induced plants. To better understand the autophagy process during systemic PCD, here we investigated the formation and type of autophagy in the root meristem cells occurring PCD. Transmission electron microscopy assay revealed that the autophagic structures formed by the fusion of vesicles, containing the sequestered cytoplasm, multilamellar bodies, and degraded mitochondria. In the PCD progress, many mitochondria appeared degradation with blurred inner membrane structure. And the endoplasmic reticulum was broke into small fragments. Finally, the damaged mitochodria were engulfed and degraded by the autophagosomes. These results indicated that during the systemic PCD process of root tip cells, the classical macroautophagy occurred, and the cell contents and damaged organelles (mitochondria) would be self-digested by autophagy.