Agriculture Reference
In-Depth Information
Fig. 7.5 Examples of selective autophagy in plants
The last example of selective autophagy shown in Fig.
7.5
deals with haem and
porphyrins degradation (Vanhee et al.
2011
). The authors indicated that the
membrane-located tryptophan-rich sensory protein (TPSO), which is induced by
various stresses, is in fact involved in haeme scavenging and targeting for degra-
dation via autophagy. TSPO has the LIR motif and co-localizes with ATG8 in plant
cells. In addition, haem-binding and functional LIR motif are necessary for
autophagy-dependent degradation of TSPO in vitro. It is probable that the TSPO
protein is also involved in binding and degradation of porphyrins, because over-
expression of TSPO in plants alleviated porphyrin-induced cytotoxity in plant cells.
Although the study still leaves many unanswered questions, such as how the plastid
- synthesised haem reaches the cytosol, it revealed the novel autophagy-based
regulatory mechanisms involved in switching off the response to stress when no
longer needed. The increased requirement for ROS scavengers (appearing as a
result of stress) leads to the increased requirements for porphyrin cofactors and
up-regulated tetrapyrrole biosynthesis. These compounds are cytotoxic and their
level needs to be carefully regulated. TSPO binds porphyrins and is along with this
cargo, degraded via autophagy.
The plant-specific ATI1 and ATI2 proteins (autophagy interacting proteins 1 and
2), identified in young seedlings upon carbon starvation were not included in
Fig.
7.5
, however they both should be considered a part of selective autophagy
