Abstract
The parasitic vines of the genus Cuscuta form haustoria that grow into other plants and connect with their vascular system, thus allowing the parasite to feed on its host. A major obstacle that meets the infection organ as it penetrates the host tissue is the rigid plant cell wall. In the present study, we examined the activity of xyloglucan endotransglucosylases/hydrolases (XTHs) during the host-invasive growth of the haustorium. The level of xyloglucan endotransglucosylation (XET) activity was found to peak at the penetrating stage of Cuscuta reflexa on its host Pelargonium zonale. In vivo colocalization of XET activity and donor substrate demonstrated XET activity at the border between host and parasite. A test for secretion of XET-active enzymes from haustoria of C. reflexa corroborated this and further indicated that the xyloglucan-modifying enzymes originated from the parasite. A known inhibitor of XET, Coomassie Brilliant Blue R250, was shown to reduce the level of XET in penetrating haustoria of C. reflexa. Moreover, the coating of P. zonale petioles with the inhibitor compound lowered the number of successful haustorial invasions of this otherwise compatible host plant. The presented data indicate that the activity of Cuscuta XTHs at the host-parasite interface is essential to penetration of host plant tissue.
Highlights
In order to sustain their own growth, parasitic plants infect other plants and absorb their nutrients
In order to compare the levels of xyloglucan endotransglucosylation (XET) activity at different stages of haustorium development in C. reflexa, enzyme extracts were made from the parasite part of swelling, penetrating and mature infections sites on the host plant P. zonale
Dot blot analysis showed that the XET activity normalized to the total protein concentration was highest when the parasite is committed to penetrating the host tissue (Fig 1)
Summary
In order to sustain their own growth, parasitic plants infect other plants and absorb their nutrients. This parasitization is accomplished by the development of the haustorium, a specialized infection organ that is able to grow into the tissue of a compatible host plant and transfer water, minerals and sugars between the two plants [1]. Species of the holoparasitic genus Cuscuta are thread-like vines that coil around potential hosts and produce haustoria to infect the aboveground parts of plants [2]. The precise mechanisms of Cuscuta host infection remain enigmatic, evidence points to cell wall changes being central [3,4,5,6].
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