Figure 2.

The regulation of autophagy and related brassinosteroid (BR) signaling pathways by PP2A. PP2A involvement is shown by red characters/arrows. TORC has various subcellular localizations in plants. We concentrate on autophagic pathways, therefore do not present here the whole signaling pathways mediated by blocking of TOR kinase signaling and by BR. Different pathways are indicated by numbers. Pathway 1: the autophagy pathway induced by inhibition of TOR kinase. The PP2A–AMPK relationship is still uncertain in plants, this is shown by a question mark. Pathway 2: induction of SBI1 methylase to remove excess BRI1. Pathway 3: induction of autophagy genes by activated BES1/BZR1, a result of BR signaling. Pathway 4: targeting of inactive BES1/BZR1 to the autophagy pathway. More details can be found in text. The upper/right part of the figure shows that during carbohydrate starvation, PP2A can be both activated and inhibited (Pathways 1 vs. 4). This may depend on the cell type dependent variation of (B and/or A) regulatory subunits. AMPK—AMP activated kinase; BR—brassinosteroid; BRI1 and BAK 1 is the BR receptor complex; LV—lytic vacuole, PM—plasma membrane. Figure was constructed with the aid of BioRender.com.