Agriculture Reference
In-Depth Information
Fig. 7.2 Macroautophagy steps. The
cup shaped
double membrane (phagophore or isolation
membrane) forms and expands trapping portions of the cell material. When the phagophore
seals and produces the (double membrane) autophagosome, this encloses the cargo, which is
transported along with the inner membrane of autophagosome into the vacuole (yeast or plants) or
into the lysosome (animals), where it is recycled
TOR Signaling Pathway and Autophagosome Biogenesis
In yeasts, animals and plants, induction of autophagy is possible after inactivating
the Target of Rapamycin (TOR) Ser/Thr kinase belonging to the family of
phosphatidynositol kinase-related kinases (Noda and Ohsumi
1998
; Pattingre
et al.
2008
; Liu and Bassham
2010
). The TOR
'
s name results from sensitivity to
macrocyclic bacterial lactone rapamycin. TOR is involved in switching cellular
responses depending on the nutritional status (John et al.
2011
). During nutrient-
rich conditions an active TOR (the TORC1 complex) consists of TOR, LST8-1,
LST8-2 and RAPTOR (Regulatory Associated Protein of TOR) (John et al.
2011
).
TORC1 together with other kinases promote anabolic processes and cell growth
while keeping autophagy switched off.
Arabidopsis
contains two RAPTOR pro-
teins, RAPTOR1A and RAPTOR1B, whose function is to recruit TOR substrate
proteins. The complex maintains the ATG1 (Autophagy Related Gene1) and
ATG13 kinases, the latter in complex with ATG17 and ATG101 accessory proteins,
dissociated through hypophosphorylation of ATG1 (one phosphorylated site) and
hyperphosporylation of ATG13 (three phosphorylated sites). In nutrient deficient
