Seed-transmitted beneficial endophytic Stagonospora sp. can penetrate the walls of the root epidermis, but does not proliferate in the cortex, of Phragmites australis

Abstract

Stagonospora sp. (4/99-1) is a beneficial endophytic fungus frequently transmitted by seeds of Phragmites australis [Cav.] Trin. ex Steudel. Here we show that this fungus also penetrates the root epidermis. At first, hyphae were attracted by the root and proliferated on the root surface, preferably over the anticlinal walls. Penetration occurred directly by undifferentiated hyphae or was facilitated by hyphopodia. Hyphal growth within the root was restricted to the walls of epidermal cells and the walls of the cells of the outermost cortical layer. Deeper growth by the fungus elicited wall appositions and ingress into the cytoplasm of cortical cells was blocked by papillae. In the rare cases, the fungus managed to penetrate into cortical cells, these reacted with necrosis. Immunological studies suggested that fungal material reached the host plasmalemma and may have been taken up by endocytotic events. Our observations explain the endophytic lifestyle of hyphae close to the epidermis and the restricted development within the cortex.Key words: Stagonospora, Phragmites australis, infection, root cortex, root epidermis.Résumé : Le Stagonospora sp. (4/99-1) est un champignon endophyte bénéfique, très souvent transmis par les semences du Phragmitis australis [Cav.] Trin. ex Steudel. On démontre ici que ce champignon pénètre également l'épiderme racinaire. Au départ, les hyphes sont attirées par la racine et prolifèrent sur la surface racinaire, préférablement sur les parois anticlines. La pénétration s'effectue directement par des hyphes indifférenciées, ou est facilitée par un hyphopode. La croissance de l'hyphe dans la racine est limitée aux parois des cellules épidermiques et de la couche corticale la plus externe. Une croissance plus en profondeur du champignon élicite des appositions pariétales et la pénétration dans le cytoplasme des cellules corticales est bloquée par des papilles. Dans les rares cas où le champignon s'est infiltré jusque dans les cellules corticales, celles-ci ont réagi avec une nécrose. Des essais immunologiques suggèrent que le matériel fongique atteint la plasmalemme de l'hôte, et pourrait été impliqué dans des évènement endocytotiques. Ces observations expliquent le mode de vie endophyte des hyphes à proximité de l'épiderme et le développement restreint dans le cortex.

Endomembrane system of aspen root cells plays a key role in defense against a common fungal root endophyte,Cryptosporiopsis radicicola

“…In the aspen-C. radicicola system hyphae grew preferentially along epidermal cell junctions, remained sparse on the host surface and penetrated the root either directly into individual cells or by pushing adjoining epidermal cells apart and growing intercellularly. A markedly similar mode of intercellular penetration was reported in the Phragmites australis-Stagonospora host-endophyte system (Gao and Mendgen 2006).…”

“…As in aspen roots, secretory vesicles participated in the formation of wall appositions in roots of Gossypium hirsutum (cotton) and P. australis (reed) after infection with Fusarium oxysporum f. sp. vasinfectum and Stagonospora respectively (Rodriguez-Gálvez andMendgen 1995, Gao andMendgen 2006). In the cortex of reed, wall appositions were enriched by callose but also included many plant components produced during normal cell wall synthesis and a walling-off phenomenon similar to that in aspen occurred (Gao and Mendgen 2006).…”

Diversity of endophytic bacteria fromEucalyptusspecies seeds and colonization of seedlings byPantoea agglomerans

“…The presence of seed microorganisms has been reported for many plant species (Granér et al , 2003; Majewska‐Sawka & Nakashima, 2004; Rudgers et al , 2004; Jordaan et al , 2006; Rudgers & Clay, 2007) and endophytic microorganisms have even been isolated from flowers (Majewska‐Sawka & Nakashima, 2004). Most studies have focused on fungal endophytic microorganisms in seeds, but few reports regarding the presence or persistence of endophytes after germination and seedling growth are available (Gao & Mendgen, 2006; Jordaan et al , 2006; Bennett & Whipps, 2007). In this study, we detected endophytic bacteria in the seeds of Eucalyptus species and bacterial presence following germination.…”

Fungal endophytes: diversity and functional roles

“…These fungi, like all endophytes, colonize plants via infection structures such as appressoria or by direct penetration of plant tissues via hyphae (Ernst et al ., 2003). Growth through plant tissues is dominantly intercellular with little to no impact on host cells (Rodriguez‐Galvez & Mendgen, 1995; Ernst et al ., 2003; Gao & Mendgen, 2006). While there may be a low level of sporulation or appressorial formation in healthy plants (Freeman & Rodriguez, 1993; Newsham, 1994), these fungi rapidly emerge and sporulate during host senescence (Weber et al ., 2004).…”