Establishment of biotrophy by parasitic plant pathogens: Candidate barley
powdery mildew effector molecules
Dale Godfrey
We have generated a library of approximately 10,000 EST sequences from barley leaf epidermal tissue,
containing a high density of powdery mildew (Blumeria graminis f.sp. hordei, Bgh) haustoria. Cluster
analysis revealed 4,327 singletons and 1,196 contigs resulting in 5,523 unigenes. In order to see which ESTs
are of plant and fungal origin, a vector machine learning filtering, combined with a manual sorting, was
performed on the unigenes and more than 3,000 haustoria-expressed unigenes were identified. Initially, ≈60
of these genes were found to encode small novel proteins (≈80-140 aa) with N-terminal signal peptides.
These are considered effector-candidates. Many of these were represented by significant numbers of ESTs,
and high haustorial gene expression was confirmed for 30 of them using RT-PCR. We subsequently re-mined
the EST-library using recursive BLAST (E-value <1 e-5, id. >30%) and have now identified ≈120 effectorcandidate genes with these features. Many of the effector-candidates appear to be transferred to the host
cytoplasm, as we have been unable to find them in the haustoria. A haustoria proteome analysis identified ca.
200 proteins, only two of them being among the effector candidates. Ongoing experiments to characterise the
function of the candidate effectors will be discussed.
Syntaxins and pathogen defence signalling
How the lesion-mimic mutant phenotype of a syntaxin double mutant uncovers novel aspects in
pathogen defence signalling
Carsten PEDERSEN, Andrea LENK, Mats ANDERSSON, Sara M. MØRCH, Mads Eggert NIELSEN,
Angela FEECHAN, Ziguo ZHANG, and Hans THORDAL-CHRISTENSEN
Plant disease resistance is the result of the collective activity of separate defence mechanisms. We have
previously discovered that the syntaxin gene SYP121 (PEN1) in Arabidopsis is required for penetration
resistance to powdery mildew fungi. SYP121 is necessary for vesicle trafficking leading to formation of
papillae, which are local cell wall appositions functioning as barriers against fungal penetration.
SYP121 has a separate function as negative regulator of other defences, which it shares with SYP122. This is
reflected in the syntaxin double mutant syp121 syp122 that has a lesion mimic phenotype. Introducing
knock-out mutations in a number of well-known defence pathways partially rescues the lesion mimic
phenotype. This shows that these pathways are active in syp121 syp122. Re-mutagenesis of syp121 syp122
has led to isolation of a large number of triple mutants with improved performance. The third mutations have
occurred in SUPPRESSOR OF SYNTAXIN-RELATED DEATH (SSD) genes, of which a number have been
identified by complementation crossings with known mutants and others have been cloned by their mapposition.
Combination of two ssd mutations often leads to an enhanced suppression of the lesion mimic phenotype,
indicating that the SSD genes control different parallel signalling pathways, each contributing to the lesion
mimic phenotype of the syp121 syp122 double mutant. By observing these combining effects among many
ssd mutant combinations we have drawn a map of signalling pathways that are active in syp121 syp122.
While most of the ssd mutants are recessive and turn out to be loss-of-function mutants we also find a few
dominant mutants and one of these has turned out to be in a gene, which encode a negative regulator of
defence signalling. This is in contrary to the majority of the SSD-genes, which are necessary for defence
signalling.