References

104 T. Nürnberger, B. Kemmerling
resistance mediated by CC-NBS-LRR resistance genes (Dangl and Jones
2001; Jones and Takemoto 2004). SGT1 and RAR1, both components of
the plant Skp1–Cullin–F-box (SCF) protein ubiquitin ligase complex (supposedly
implicated in the removal of negative regulator plant resistance
pathways), have been implicated in innate immunity both at the plant
species and the plant cultivar level (Azevedo et al. 2002; Peart et al. 2002;
Takahashi et al. 2003).
7.6
Conclusions and Future Prospects
The last decade has seen an enormous increase in the knowledge base
on plant innate immunity. Cloning and characterization of more than 50
plant resistance genes and isolation of the first genes encoding plant PAMP
receptors are among those achievements. Establishment and proof of the
“guard hypothesis” and elucidation of the role of microbial effector proteins
in susceptible (virulence factors) and resistant host plant cultivars
(Avr factors) has further helped us to reconcile the concepts of PAMPbased
immunity and R gene-dependent cultivar-specific plant immunity.
Importantly, conceptual and structural similarities in the molecular organization
of plant and animal innate immunity have been unraveled. While
these findings underline the requirement for non-self-recognition and rejection
in all multicellular eukaryotic organisms, the currently available
data set supports independent, convergent evolution of innate immunity
in plants and animals.
In the future, a combination of powerful genetic screens and reverse genetics
approaches, protein–protein interaction studies and genomic analyses
(the latter based upon an increasing number of fully sequenced microbial
genomes, including those from closely related pathovars) will significantly
enhance the number of elements implicated in plant innate immunity.
A more complete picture of the molecular basis of the two faces of this
phenomenon (plant species and plant cultivar-specific innate immunity)
will enable us to determine the genetic requirements that are common
or specific to either type of plant immunity. Moreover, understanding the
molecular organization of durable plant species immunity is likely to open
avenues towards genetic engineering of durable pathogen resistance in crop
plants.
References
Aderem A, Ulevitch R (2000) Toll-like receptors in the induction of the innate immune
response. Nature 406:782–787