Agriculture Reference
In-Depth Information
ATG18a
are more sensitive to high salt and drought than the wild-type plants,
demonstrating a role for autophagy in the response to these stresses (Liu
et al.
2009
). The same authors also reported that induction of autophagy upon
nutrient starvation and salt stress depends on the activity of plasma membrane
NADPH oxidase and that induction of autophagy upon osmotic stress (caused by
mannitol) is NADPH oxidase-independent.
Nutrient deficit up-regulates autophagy. For example, induced transcription of
some
ATG
genes (e.g.
ATG4
,
ATG8a-i
,
ATG3
,
ATG7
) was observed upon C
starvation in
Arabidopsis
(Rose et al.
2006
), and of
ATG8
upon N and sulfur
starvation in tobacco (Zientara-Rytter et al.
2011
). Additionally, some
atg
mutants
(e.g.
atg7
,
atg5
,
atg10
) are hypersensitive to nutrient deficit (Li and Vierstra
2012a
).
Autophagy participation in plant responses to other nutrient stresses such as
phosphorus or iron starvation has been discussed only in the context of participating
Ub-ligases and the UPS (Lyzenga and Stone
2012
; Rojas-Triana et al.
2013
).
However, no attempts to test the role of autophagy in this process were undertaken.
Interestingly, it has been recently reported that sulfide, which is generated from
cysteine by cysteine desulfhydrase in the cytosol of
Arabidopsis
plants, acts as a
negative regulator of autophagy and that this effect is independent from the sulfur
status of the plant (Alvarez et al.
2012a
,
b
). Such a conclusion came from the
observation that plants defective in the activity of cysteine desulfhydrase (
des1
mutants) show premature leave senescence and increased expression of senescence
associated genes. In addition, externally added hydrogen sulfide was able to alle-
viate some of the observed phenotypes. The mechanism of action of sulfide is
completely unknown. However, the authors suggested that some enzymes neces-
sary for autophagy process might be possible targets of such regulation
(e.g. through reversible S-thiolation), for example E1 and E2 enzymes involved
in ubiquitination or ATG4 cysteine protease. It is worthwhile mentioning that
hydrogen sulfide is already recognised as an important signaling molecule in
mammalian systems (Lowicka and Beltowski
2007
; Szabo
2007
; Gadalla and
Snyder
2010
).
In conclusion, autophagy is an important process involved in plant response to
nutritional stresses. Emerging data suggest that the controlled enhancement of
autophagy can be exploited for improvement of crop performance in normal and
nutrient-limiting conditions.
Selective Autophagy
The process of selective autophagy was first described in yeast (see above, CVT).
Paradoxically, this process is a part of biosynthetic pathway and it is involved in a
selective delivery of two lysosomal enzymes to the vacuole described neither for
animals nor plants (Lynch-Day and Klionsky
2010
). As mentioned before, a
number of organelles, storage structures, pathogens or protein aggregates are
