SummaryConfocal microscopy of amphiphilic styryl dyes has been used to investigate endocytosis and vesicle trafficking in living fungal hyphae. Hyphae were treated with FM4-64, FM1-43 or TMA-DPH, three of the most commonly used membrane-selective dyes reported as markers of endocytosis. All three dyes were rapidly internalized within hyphae. FM4-64 was found best for imaging the dynamic changes in size, morphology and position of the apical vesicle cluster within growing hyphal tips because of its staining pattern, greater photostability and low cytotoxicity. FM4-64 was taken up into both the apical and subapical compartments of living hyphae in a time-dependent manner. The pattern of stain distribution was broadly similar in a range of fungal species tested (Aspergillus nidulans, Botrytis cinerea, Magnaporthe grisea, Neurospora crassa, Phycomyces blakesleeanus, Puccinia graminis, Rhizoctonia solani, Sclerotinia sclerotiorum and Trichoderma viride). With time, FM4-64 was internalized from the plasma membrane appearing in structures corresponding to putative endosomes, the apical vesicle cluster, the vacuolar membrane and mitochondria. These observations are consistent with dye internalization by endocytosis. A speculative model of the vesicle trafficking network within growing hyphae is presented.
SummaryPlant immunity against the majority of the microbial pathogens is conveyed by a phenomenon known as non-host resistance (NHR). This defence mechanism affords durable protection to plant species against given species of phytopathogens. We investigated the genetic basis of NHR in Arabidopsis against the wheat powdery mildew fungus Blumeria graminis f. sp. tritici (Bgt). Both primary and appressorial germ tubes were produced from individual Bgt conidia on the surface of the Arabidopsis leaves. Attempted infection occasionally resulted in successful penetration, which led to the development of an abnormal unilateral haustorium. Inoculation of a series of Arabidopsis defence-related mutants with Bgt resulted in the attenuation of reactive oxygen intermediate (ROI) production and salicylic acid (SA)-dependent defence gene expression in eds1, pad4 and nahG plants, which are known to be defective in some aspects of host resistance. Furthermore, Bgt often developed bilateral haustoria in the mutant Arabidopsis lines that closely resembled those formed in wheat. A similar decrease in NHR was observed following treatment of the wild-type Arabidopsis plants with cytochalasin E, an inhibitor of actin micro®lament polymerisation. In eds1 mutants, inhibition of actin polymerisation severely compromised NHR in Arabidopsis against Bgt. This permitted completion of the Bgt infection cycle on these plants. Therefore, actin cytoskeletal function and EDS1 activity, in combination, are major contributors to NHR in Arabidopsis against wheat powdery mildew.
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