Anthocyanin Vacuolar Inclusions Form by a Microautophagy Mechanism

作者：Chanoca Alexandra; Kovinich Nik; Burkel Brian; Stecha Samantha; Bohorquez Restrepo Andres; Ueda Takashi; Eliceiri Kevin W; Grotewold Erich; Otegui Marisa S^*

来源：Plant Cell, 2015, 27(9): 2545-2559.

DOI：10.1105/tpc.15.00589

Anthocyanins are flavonoid pigments synthesized in the cytoplasm and stored inside vacuoles. Many plant species accumulate densely packed, 3- to 10-mm diameter anthocyanin deposits called anthocyanin vacuolar inclusions (AVIs). Despite their conspicuousness and importance in organ coloration, the origin and nature of AVIs have remained controversial for decades. We analyzed AVI formation in cotyledons of different Arabidopsis thaliana genotypes grown under anthocyanin inductive conditions and in purple petals of lisianthus (Eustoma grandiorum). We found that cytoplasmic anthocyanin aggregates in close contact with the vacuolar surface are directly engulfed by the vacuolar membrane in a process reminiscent of microautophagy. The engulfed anthocyanin aggregates are surrounded by a single membrane derived from the tonoplast and eventually become free in the vacuolar lumen like an autophagic body. Neither endosomal/prevacuolar trafficking nor the autophagy ATG5 protein is involved in the formation of AVIs. In Arabidopsis, formation of AVIs is promoted by both an increase in cyanidin 3-O-glucoside derivatives and by depletion of the glutathione S-transferase TT19. We hypothesize that this novel microautophagy mechanism also mediates the transport of other flavonoid aggregates into the vacuole.

• 出版日期2015-9