PHIDIAS: Pathogen-Host Interaction Data Integration and Analysis System

Phinet Name: Phakopsora pachyrhizi
Phinet Information
Pathogen Name: Phakopsora pachyrhizi
Pathogen NIAID Category: Others
Bio-objects
Bio-object 1: Appressoria
Location: Extracellular Function: Other Description: Appressoria develops over anticlinal walls, the center of epidermal cells or, rarely, over stomata(<a href="#reference5423">Koch</a>)
Bio-object 2: Appressorial cone
Location: Extracellular Function: Other Description: Penetration of the leaves started with the formation of a funnel-shape structure in the appressorium. Similar structures were observed in other fungal parasites and named"appressorial cone". We use this term tentatively with the recognition that there are morphological differences in the structure of the appressorial cone of different fungi.Penetration of the leaves always occurred directly through the cuticle.(<a href="#reference5423">Koch</a>)
Bio-object 3: Germ tube
Location: Extracellular Function: Other Description: Germ tubes varied from 5 to 400 microns (Koch and Hoppe, 1988). Urediospores germ tubes that do not form infection structures die within a few days (Heath, 1995).(<a href="#reference5424">KochE</a>)
Bio-object 4: Haustoria
Location: Intracellular Function: Other Description: Biotrophic plant pathogenic fungi differentiate specialized infection structures within the living cells of their host plants. These haustoria have been linked to nutrient uptake ever since their discovery. We have for the first time to our knowledge shown that the flow of sugars from the host Vicia faba to the rust fungus Uromyces fabae seems to occur largely through the haustorial complex (Voegele et al., 2001). Formation of the first haustorium ocurred between 24 and 48 hpi. The fungus continues to spread rapidily through the tissue forming a dense mycelium, filling the intercellular space and inserting haustoria into mesophyll and epidermal cells. One cell often contained two or more haustoria. Haustorial formation resembled that known from other rust fungi (Koch et al., 1983).(<a href="#reference5423">Koch</a>)(<a href="#reference5422">Voegele et al., 2001</a>)
Bio-object 5: Haustoria mother cell (HMC)
Location: Intracellular Function: Other Description: Haustoria mother cell was was delimited by a septum from the intercellular mycelium contained two nuclei and appeard closely appressed to the host wall in the region of penetration.(<a href="#reference5423">Koch</a>)
Bio-object 6: Infection peg
Location: Intracellular Function: Other Description: At the site of host cell penetration the haustorial mother cell was thickened. The host cell wall was breaced by a thin infection peg originating from the inner layer of the haustorial mother cell wall. The infection peg expanded to form an haustorial neck which had an electron opaque neckband and terminated in the haustorial body.(<a href="#reference5423">Koch</a>)
Bio-object 7: Mycelium
Location: Other Function: Other Description: Three days post infection (dpi) a considerably amount of mycelium had developed in the spongy mesophyll. In the center of these mycelial conglomerates epidermal and mesoophyll cells of the host became necrotic giving rise to lesions which were macroscopically visible 6 dpi. Lateral spread of the fungus commonly continued by the formation of hyphae resembling runner hyphae of cereal rusts.Hyphal spread was restricted by leaf veins. Minor veins were often crossed, but larger vascular bundles stopped the spread of the fungus.(<a href="#reference5423">Koch</a>)
Bio-object 8: Penetration hypha
Location: Cytoplasm Function: Other Description: The development of the penetration hypha resulted from the elongation of the appressorial cone (Koch et al.,1983). The penetration hyphae emerged from the floor of the appressorium where the latter contacted the membrane surface. Apparently, this event corresponds to the"directional peg emergence" observed in the stomata entering rust fungi (Koch and Hoppe, 1988).The hypha penetrates the epidermal cell wall of the host, transversed the cell and reached the intercellular space of the spongy or pallisade mesophyll where the first septum was formed delimiting the penetration hypha from the primary hypha. Transversing of the epidermal cell was completed about 20 hpi (Koch et al., 1983).(<a href="#reference5423">Koch</a>)(<a href="#reference5424">KochE</a>)
Bio-object 9: Primary hyphae or infection hyphae
Location: Intercellular Function: Other Description: Intercellular growth strated with the formation of the first septum delimiting the penetration hyphae from the Infection hyphae (Heath) or primary hypha (Koch) : the latter then branced to form secondary hyphae.(<a href="#reference5423">Koch</a>)(<a href="#reference5420">Heath</a>)
Bio-object 10: Uredia formation
Location: Other Function: Other Description: Uredia were commonly formed in the spongy mesophyll, liberating the spores on the lower surface of the leaf. Similar to other rust fungi, the first evidence of uredia formation in P. pachyrhizi was the aggregation of hyphae into uredial prinordia. Those structures were first visible 8dpi. Uredospore production started 3-4 days later through a uredial opening lined with several layers of clavate, paraphysoid cells, that obviously derived from the outer cell layers of developing uredia. When the uredium matures, the epidermis ruptures and uredospores are released(<a href="#reference5423">Koch</a>)
Bio-object 11: Uredospores
Location: Other Function: Other Description: Formation of uredospores is based on a sporogenous cell which by budding and septum formation produces a spore initial. By a second septum the uredospore initial is separated into a proximal pedicel and a distal, immature uredospore. It results in a column-like series of three cells lying one upon the other: the sporogenous cell, the pedicell , and the uredospore . The mechanism of uredospore development has been observed with different Pucciniaceae and Melampsoraceae(<a href="#reference5423">Koch</a>)
Bio-object 12: Uredospores (=Urediospores)
Location: Extracellular Function: Other Description: Observation of whole-leaf mounts revealed that 12 hours post infection (hpi) the majority of spores had germinated (Koch et al., 1983).(<a href="#reference5423">Koch</a>)
Interactions
Interaction 1: Interaction1
Input Objects: Uredospores (=Urediospores) Output Objects: Germ tube GO Evidence Code: No biological Data available Description: When uredospores of P. pachyrhizi were germinated on water agar, germ tubes grew without forming appressoria. In contrast, a high percentage of germ tubes form appresssoria in contact with dyalisis membrane.(<a href="#reference5424">KochE</a>)
Interaction 2: Interaction2
Input Objects: Germ tube Output Objects: Appressoria GO Evidence Code: No biological Data available Description: When membrane filters differing in surface topography were inoculated with P. pachyrhizi, appresorium formation only accur if the filter surface provides sufficient footing for the germ tube so that intimate contact could be established. As for the stomata penetrating rusts,"germ tube adherence" clearly is a prerequsite for induction of infection structures and, thus, infection of the host by P. pachyrhizi (Koch and Hoppe, 1988). Recognition of topographic signal by fungal germ tubes or hyphae is termed thigmotropism (Allen et al., 1990). Apressoria formation was unequivocally triggered by thigmotropic stimuli. P. pachyrhizi has a wide host range, and appressoria were formed at high rates on nonhosts such as wheat, lettuce, and potato and may even be formed on glass slides. These observations indicate that the formation of appresssoria is easily induced and that the stimuli causing thigmodifferentiation are more unspecific compared to those required for germ tube differentiation by the stomate penetrating rust fungi (Koch and Hoppe, 1988). Other authors concluded that, although P. pachyrhizi is capable of forming appressoria in the absence of topographical signals, surface topography is likely involved in the location of penetration sites (Allen et al., 1990).(<a href="#reference5424">KochE</a>)(<a href="#reference5418">Allen</a>)
Interaction 3: Interaction3
Input Objects: Appressoria Output Objects: Appressorial cone GO Evidence Code: No biological Data available Description: Penetration started with the formation of a funnel-shaped structutre in the appresssorium, which was visible 12hpi. Similar stuctures were observed previously in the appresssoria of other fungal parasites and named"appressorial cone". We use this name tentatively with the recognition that there are morphological differences in the strucuture of the appressorial cone of different fungi. The appressorial cone originated within the apppressorium as a branched cell wall-like structure(<a href="#reference5423">Koch</a>)
Interaction 4: Interaction4
Input Objects: Appressorial cone Output Objects: Penetration hypha GO Evidence Code: No biological Data available Description: Penetration of the leaves by uredospore-derived infection structures of P. pachyrhizi in this study always occurred directly through the cuticle. According to our results, stomata penetration can almost be excluded, since it could be shown that, when an appressorium has been formed over a stomata, the fungus infected one of the guard cells but did not enter the leaf througout the stomatal opening.(<a href="#reference5423">Koch</a>)
Interaction 5: Interaction5
Input Objects: Penetration hypha Output Objects: Primary hyphae or infection hyphae GO Evidence Code: No biological Data available Description: The penetration hyphae elongated and formed a branched or unbranched primary hyphae (Koch and Hoppe, 1988).The development of the penetration hyphae obviously resulted from the elongation of the appresssorial cone. After inoculation of different plant species with uredospores of the soybean rust fungi, penetration hypha development was much lower than the appressorium formation. Development of the penetration hypha seems to be the most critical point during infection structure development. Apparently, a second stimuli is required to trigger the formation of the penetration hypha. However the nature of the inducing stimulus is not known (Koch and Hoppe, 1988).In our study the penetration hyphae arising from the appresssorium transversed the lumen of the epidermal cell and entered the intercellular space where the first septum was formed (Koch and Hoppe, 1983).The epidermal cell initially invaded by the fungus showed early signs of disorganization (24 hpi). Collapse of the epidermal cell coincided with an increase in size of the penetration hyphae and the penetration pores in the epidermal cell wall (Koch and Hoppe, 1988).(<a href="#reference5423">Koch</a>)(<a href="#reference5424">KochE</a>)
Interaction 6: Interaction6
Input Objects: Primary hyphae or infection hyphae Output Objects: Mycelium, Haustoria mother cell (HMC) GO Evidence Code: No biological Data available Description: According to Heath, it seems that infection hyphae ( or primary hyphae) of the rust fungi either lack elicitors of defences specific to their host species or they suppress these defenses with plant specific suppressors. Much more research is needed before we fully understand how each rust fungus prevents nonspecific defense responses of its host plant (Heath, 1995).Treatment of broad bean leaves with salicylic acid (SA) or 2,6-dichloro-isonicotinic acid (DCINA) induces resistance against the rust fungus Uromyces fabae resulting in reduced rust pustule density. Light-microscopy studies showed that in induced resistant plants the rust fungus is inhibited immediately after penetration through the stomatal pore. The differentiation of infection structures growing within the intercellular space of the leaf, i.e. infection hyphae and haustorial mother cells, is inhibited. Furthermore, low-temperature scanning electron microscopy studies of freeze fractures revealed protrusions at the tips of infection hyphae growing in induced resistant broad bean leaves. Treatment of in vitro-differentiating rust infection structures with intercellular fluids (IFs) from induced resistant plants confirmed that the fungus is sensitive towards an apoplastic anti-fungal activity only after having formed appressoria. Other legume rusts such as U. vignae and U. appendiculatus were likewise inhibited in the presence of IF from SA-treated broad bean leaves. Heterologous antibodies were used to study changes in the extracellular pathogenesis-related (PR) protein pattern after resistance induction. Western blots indicated that chitinases and beta-1,3-glucanases were present in both induced and control plants. In contrast, PR-1 proteins were newly synthesized in response to SA or DCINA application. The major induced PR-1 protein was purified and exhibited strong differentiation-inhibiting activity towards U. fabae infection structures. We conclude that the inhibition of rust infection hyphae in acquired resistant broad bean plants is mainly due to the anti-fungal activity of this induced basic PR-1 protein (Rauscher el al., 1999).(<a href="#reference5424">KochE</a>)
Interaction 7: Interaction7
Input Objects: Mycelium Output Objects: Uredia formation GO Evidence Code: No biological Data available Description: Similar to other rust fungi, the first evidence of uredia formation in P. pachyrhizi was the aggregation of hyphae into uredial prinordia(<a href="#reference5423">Koch</a>)
Interaction 8: Interaction8
Input Objects: Uredia formation Output Objects: Uredospores GO Evidence Code: No biological Data available Description: Uredospore production started 3-4 days later through a uredial opening lined with several layers of clavate, paraphysoid cells, that obviously derived from the outer cell layers of developing uredia>Hyphal spread was restricted by leaf veins. Minor veins were often crossed but larger vascular bundles stopped the spread of the fungus. Occasionally, a few hyphae were observed spreading into adjacent interveinal areas (Koch et al., 1983)(<a href="#reference5423">Koch</a>)
Interaction 9: Interaction9
Input Objects: Haustoria mother cell (HMC) Output Objects: Infection peg GO Evidence Code: No biological Data available Description: Haustorial mother cell (HMC) preceeded the formation of the haustoria. It was delimited by a septum from the intercellular mycellium, contained two nuclei and appeared closely appressed to the host wall in the region of penetration (Koch and Hoppe, 1983).For rust fungi, Heath suggested that formation of haustorial mother cell is elicited by the plant cell surface (Heath, 1995).(<a href="#reference5423">Koch</a>)(<a href="#reference5420">Heath</a>)
Interaction 10: Interaction10
Input Objects: Infection peg Output Objects: Haustoria GO Evidence Code: No biological Data available Description: Examination of whole- leaf mounts and semi-thin sections, suggested that some haustoria were encased by a dense material. The material was stained, indicating the presence of callose. Encapsulation seemed to occur at early stages of haustorial development.(Koch and Hoppe, 1983)The present work strongly suggests that active D-glucose and D-fructose uptake in the biotrophic mycelium of the rust fungus U. fabae occurs at least preferentially, if not exclusively, via specialized infection structures, the haustoria. The differences found regarding the affinity of the transporter for different substrates is consistent with the earlier findings of D-glucose being the preferred sugar over sucrose.The ability of HXT1p from U. fabae to transport D-glucose and D-fructose and the restricted localization to the haustorial plasma membrane leaves only the extrahaustorial matrix as a source for sugars. This work therefore presents compelling evidence for a role of the haustorial complex of rust fungi in sugar uptake. (Voegele, 2001).According to Heath, haustorium on rust fungi, suppresses callose deposition and other cell wall modifications, elicits nuclear migration and changes in plant membrane, and produces cultivar-specific elicitors of resistance responses such as cell death or encasement. (Heath, 1995).(<a href="#reference5424">KochE</a>)(<a href="#reference5420">Heath</a>)(<a href="#reference5422">Voegele et al., 2001</a>)
Pathways

Phinet Name: Phakopsora pachyrhizi