Chemistry Reference
In-Depth Information
overproduction. There is another possible scenario: infection induces the SA
synthesis which induces the synthesis of callose and PDLP5. The effect is
enhanced by PDLP5, which, in turn, induces the formation of additional
amounts of SA. Callose and PDLP5 together clog plasmodesmata and isolate the
infected cell. That is, PDLP5 plays an important role in controlling the plas-
modesma conductivity during the salicylic acid-mediated cell death responses
Cytoplasmic proteins. Recently, more and more cytoplasmic protein factors
involved in the regulation of plasmodesma conductivity are opened. Some of them
function in coordination with callose. Among such proteins is ankyrin repeat-
containing protein (ANK), a cellular factor facilitating transport of nucleoprotein
complex between the cells. It is known that, in order to facilitate the passage
through the plasmodesmata, TMV-type viruses produce a movement protein,
which forms a complex with viral RNA. This nucleoprotein complex binds to the
plasmodesmata and increases their conductivity, ensuring the transfer of the
complex in a neighboring cell. ANK interferes with this interaction. In mutants
overexpressing ANK, virus spreading is enhanced. Conversely, a weak expression
of this protein inhibited the spread of viral infection (Ueki et al.
2010
). It is
possible that ANK interaction with the movement protein explains to a certain
extent the long known capacity of the latter to improve the conductivity of the
plasmodesmata. It is suggested that ANK binds to the viral protein on plasmo-
desmata and to the cytoplasmic domain of some subunits of transmembrane cal-
lose synthase. As a result, the callose synthesis is suppressed; its content in the
vicinity of plasmodesmata decreases, plasmodesma conductance increases, and
virus transport is enhanced. Such a possibility of cytoplasmic protein ANK to
facilitate the penetration of viral ribonucleic complex through the plasmodesmata
may be in use for symplastic transport of their own molecules. Some endogenous
plant proteins are known, which, like viral movement protein, can improve plas-
modesmal conductivity. It is possible that they also involve ANK in the interaction
with plasmodesmata.
Comparing these methods of regulation of plasmodesmal conductivity, we can
see that in most cases the end result is changing the content of callose. Protein
factors, salicylic acid, and calcium combine their efforts in the stimulation or
inhibition of callose deposition at plasmodesmata. In the case of the stimulatory
effect, not only the isolation of damaged areas of tissue is achieved, but also isolated
symplastic domains are formed, which is a step in the plant development. The
inhibitory effect of these compounds on callose synthesis contributes to the intense
exchange between cells and tissues of assimilates, hormonal substances, and other
signaling molecules that needs to coordinate their functions at intence growth.
Search WWH ::
Custom Search