Dodder hyphae invade the host: a structural and immunocytochemical characterization

Abstract

Dodder (Cuscuta pentagona) hyphae are unique amongst the parasitic weeds for their ability to apparently grow through the walls of the host plant. Closer examination reveals, however, that the hyphae do not grow through the host but rather induce the host to form a new cell wall (or extend the existing wall) to coat the growing hypha. This chimeric wall composed of walls from two species is even traversed by plasmodesmata that connect the two cytoplasms. Compositionally, the chimeric wall is quite different from the walls of either the host or in other cells of the dodder plant, on the basis of immunocytochemical labeling. The most striking differences were in the pectins, with much stronger labeling present in the chimeric wall than in either the host or other dodder walls. Interestingly, labeling with monoclonal antibodies specific to arabinan side chains of rhamnogalacturonan I pectin fraction was highly enriched in the chimeric wall, but antibodies to galactan side chains revealed no labeling. Arabinogalactan protein antibodies labeled the plasma membrane and vesicles at the tips of the hyphae and the complementary host wall, although the JIM8-reactive epitope, associated with very lipophilic arabinogalactan proteins, was found only in dodder cells and not the host. Callose was found in the plasmodesmata and along the forming hyphal wall but was found at low levels in the host wall. The low level of host wall labeling with anticallose indicates that a typical woundlike response was not induced by the dodder. When dodder infects leaf lamina, which have more abundant intercellular spaces than petioles or shoots, the hyphae grew both intra- and extracellularly. In the latter condition, a host wall did not ensheath the parasite and there was clear degradation of the host middle lamellae by the growing hyphae, allowing the dodder to pass between cells. These data indicate that the chimeric walls formed from the growth of the host cell wall in concert with the developing hyphae are unique in composition and structure and represent an induction of a wall type in the host that is not noted in surrounding walls.

Interspecific RNA Interference of SHOOT MERISTEMLESS-Like Disrupts Cuscuta pentagona Plant Parasitism

“…Seedlings have a short-lived rudimentary root system, lack enough reserves for sustained growth, and contain little chlorophyll and thus are completely dependent on finding a host within a few days for survival. At points of contact with the host, the coiled dodder stem produces haustoria that penetrate host tissues and form vascular connections (Kuijt, 1983;Vaughn, 2003). Haustoria produce long, unicellular searching hyphae that make many plasmodesmata at the contact point with host parenchyma (Vaughn, 2003;Birschwilks et al, 2006).…”

“…At points of contact with the host, the coiled dodder stem produces haustoria that penetrate host tissues and form vascular connections (Kuijt, 1983;Vaughn, 2003). Haustoria produce long, unicellular searching hyphae that make many plasmodesmata at the contact point with host parenchyma (Vaughn, 2003;Birschwilks et al, 2006). Eventually, phloem-phloem and xylem-xylem connections formed between dodder and the host are used to transfer water and assimilates to the parasite (Jeschke et al, 1994;Vaughn, 2003;Birschwilks et al, 2006).…”

Inhibition of pectin methyl esterase activity by green tea catechins

“…Regulation of PME activity by endogenous protein inhibitors may be altered during tissue invasion processes that require cell wall degradation, for example, during host invasion by plant parasites (Ben-Hod et al, 1993;Losner-Goshen et al, 1998;Nagar et al, 1984;Vaughn, 2003;Veronesi et al, 2005). Plants resistant to invasion appear to exhibit strong inhibition of cell wall degrading enzymes at tissue surfaces (Singh and Singh, 1997).…”

Ultrastructural Immunolocalization of Arabinogalactan Protein, Pectin and Hemicellulose Epitopes Through Anther Development inBrassica napus

“…There seems to be a replacement of arabinans by galactans, at least in the epidermis, possibly due to the de novo synthesis of pectins and/or to their in situ remodeling. In general, abundance of LM6-recognized epitopes is associated to rapidly growing cells, whereas abundance of LM5-recognized epitopes seems to be associated to maturing tissues (Vaughn 2003). Previous studies have related the increase of galactose side-chains in pectins of differentiating and elongating cells with the increase in cell wall firmness (Majewska-Sawka et al 2004;McCartney et al 2000;McCartney et al 2003;Willats et al 1999).…”