Cuscuta seeds: Diversity and evolution, value for systematics/identification and exploration of allometric relationships.

Cuscuta (dodders) is a group of parasitic plants with tremendous economic and ecological significance. Their seeds are often described as "simple" or "unspecialized" because they do not exhibit any classical dispersal syndrome traits. Previous studies of seed morphology and/or anatomy were conducted on relatively few species. We expanded research to 101 species; reconstructed ancestral character states; investigated correlations among seed characters and explored allometric relationships with breeding systems, the size of geographical distribution of species in North America, as well as the survival of seedlings. Seed morphological and anatomical characters permit the separation of subgenera, but not of sections. Identification of Cuscuta species using seed characteristics is difficult but not impossible if their geographical origin is known. Seeds of subg. Monogynella species, exhibit the likely ancestral epidermis type consisting of elongated and interlocked cells, which are morphologically invariant, uninfluenced by dryness/wetness. Subgenera Cuscuta, Pachystigma and Grammica have evolved a seed epidermis with isodiametric cells that can alternate their morphology between two states: pitted when seeds are dry, and papillose after seed imbibition. A seed coat with double palisade architecture throughout the entire seed has also apparently evolved in subgenera Cuscuta, Pachystigma and Grammica, but several species in two clades of the latter subgenus reverted to a single palisade layer outside the hilum area. The same latter species also evolved a peculiar, globose embryo, likely having a storage role, in contrast to the ancestral filiform and coiled embryo present throughout the remainder of the genus. Autogamous species had on average the highest number of seeds per capsule, whereas fully xenogamous taxa had the lowest. No correlation was revealed between the size of the seeds and the size of their geographical distribution in North America, but seedlings of species with larger seeds survived significantly longer than seedlings resulted from smaller seeds. Diversity and evolution of seed traits was discussed in relationship with their putative roles in dormancy, germination and dispersal.

Organization of Vascular Cells in the Haustorium of the Parasitic Flowering Plant Cuscuta japonica.

The stem parasite dodder, Cuscuta japonica, has evolved a specialized root-like organ, the haustorium, which is differentiated from the stem. In order to take up water and nutrients, C. japonica reprograms haustorial cells to vascular cells, connecting the host's vascular system to its own. However, little is known about vascular differentiation in haustoria. In this study, we first confirmed the temporal and spatial expression profiles of vascular cell type-specific genes, CjAPL, CjSEOR1, CjWOX4 and CjTED7, to examine whether phloem companion cells, developing sieve elements, procambial cells and differentiating xylem cells, respectively, are present in the haustoria. CjAPL and CjSEOR1 decreased, and CjWOX4 showed a transient increase before the onset of xylem vessel formation, and then decreased. CjTED7 increased coincidentally with xylem vessel formation. In situ hybridization demonstrated that CjWOX4-expressing cells and phloem-conducting cells are in close proximity, and occupied a domain distinguishable from xylem vessels, suggesting differentiation of a phloem/procambial domain and a xylem domain in the haustorium. Secondly, expression of regulatory genes that are involved in determination of the fate of procambial cells was investigated. Expression patterns of CjCLE41, CjGSK3 and CjBES1suggested that TDIF-TDR-GSK3-mediated signaling is activated in haustoria. The natural antisense transcript of CjCLE41 was detected in haustoria, implying the sense regulation of CjCLE41. Expression profiles of the regulatory genes, combined with those of cell type-specific marker genes, suggest that reprogramming of haustorial cells to vascular cells is regulated in a way that allows the immediate formation of xylem vessels by alleviating inhibition of xylem differentiation.

Waterfowl endozoochory: An overlooked long-distance dispersal mode for Cuscuta (dodder).

PREMISE OF THE STUDY: Dispersal of parasitic Cuscuta species (dodders) worldwide has been assumed to be largely anthropomorphic because their seeds do not match any previously known dispersal syndrome and no natural dispersal vectors have been reliably documented. However, the genus has a subcosmopolitan distribution and recent phylogeographic results have indicated that at least18 historical cases of long-distance dispersal (LDD) have occurred during its evolution. The objective of this study is to report the first LDD biological vector for Cuscuta seeds. METHODS: Twelve northern pintails (Anas acuta) were collected from Suisun Marsh, California and the contents of their lowest part of the large intestine (rectum) were extracted and analyzed. Seed identification was done both morphologically and using a molecular approach. Extracted seeds were tested for germination and compared to seeds not subjected to gut passage to determine the extent of structural changes caused to the seed coat by passing through the digestive tract. KEY RESULTS: Four hundred and twenty dodder seeds were found in the rectum of four northern pintails. From these, 411 seeds were identified as Cuscuta campestris and nine as most likely C. pacifica. The germination rate of C. campestris seeds after gut passage was 55%. Structural changes caused by the gut passage in both species were similar to those caused by an acid scarification. CONCLUSIONS: Endozoochory by waterbirds may explain the historical LDD cases in the evolution of Cuscuta. This also suggests that current border quarantine measures may be insufficient to stopping spreading of dodder pests along migratory flyways.

Getting ready for host invasion: elevated expression and action of xyloglucan endotransglucosylases/hydrolases in developing haustoria of the holoparasitic angiosperm Cuscuta.

Changes in cell walls have been previously observed in the mature infection organ, or haustorium, of the parasitic angiosperm Cuscuta, but are not equally well charted in young haustoria. In this study, we focused on the molecular processes in the early stages of developing haustoria; that is, before the parasite engages in a physiological contact with its host. We describe first the identification of differentially expressed genes in young haustoria whose development was induced by far-red light and tactile stimuli in the absence of a host plant by suppression subtractive hybridization. To improve sequence information and to aid in the identification of the obtained candidates, reference transcriptomes derived from two species of Cuscuta, C. gronovii and C. reflexa, were generated. Subsequent quantitative gene expression analysis with different tissues of C. reflexa revealed that among the genes that were up-regulated in young haustoria, two xyloglucan endotransglucosylase/hydrolase (XTH) genes were highly expressed almost exclusively at the onset of haustorium development. The same expression pattern was also found for the closest XTH homologues from C. gronovii. In situ assays for XTH-specific action suggested that xyloglucan endotransglucosylation was most pronounced in the cell walls of the swelling area of the haustorium facing the host plant, but was also detectable in later stages of haustoriogenesis. We propose that xyloglucan remodelling by Cuscuta XTHs prepares the parasite for host infection and possibly aids the invasive growth of the haustorium.

Differential effects of ephemeral colonization by arbuscular mycorrhizal fungi in two Cuscuta species with different ecology.

Seedlings of parasitic Cuscuta species are autotrophic but can survive only a short period of time, during which they must locate and attach to a suitable host. They have an ephemeral root-like organ considered not a "true" root by most studies. In the present study, two species with contrasting ecology were examined: Cuscuta gronovii, a North American riparian species, and Cuscuta campestris, an invasive dodder that thrives in disturbed habitats. The morphology, structure, and absorptive capability of their root-like organ were compared, their potential for colonization by two species of arbuscular mycorrhizal fungi (AMF) was assessed, and the effect of the AMF on seedling growth and survival was determined. The root of both species absorbed water and interacted with AMF, but the two species exhibited dissimilar growth and survival patterns depending on the colonization level of their seedlings. The extensively colonized seedlings of C. gronovii grew more and survived longer than non-colonized seedlings. In contrast, the scarce colonization of C. campestris seedlings did not increase their growth or longevity. The differential growth responses of the AMF-colonized and non-colonized Cuscuta species suggest a mycorrhizal relationship and reflect their ecology. While C. gronovii roots have retained a higher ability to interact with AMF and are likely to take advantage of fungal communities in riparian habitats, the invasive C. campestris has largely lost this ability possibly as an adaptation to disturbed ecosystems. These results indicate that dodders have a true root, even if much reduced and ephemeral, that can interact with AMF.

[Micromorphological comparative identification between several Chinese herbal medicines and their counterfeits].

OBJECTIVE: To identify comparatively several commercial Chinese herbal medicines and their counterfeits. METHOD: The micromorphological characters were identified. The shape, surface, section and other characters of the medicinal materials were identified by using anatomical lens and scanning apparatus. Pictures were taken and saved. RESULT: Main micromorphological differences between several Chinese herbal medicine including Lonicera macranthoides, L. similis, Cuminum cyminum, Plantago asiatica, Cuscuta chinensis, Sinapis alba, Salvia miltiorrhiza and their counterfeits were identified. CONCLUSION: The reference for the authenticity identification of Chinese herbal medicine and helpful experiences for the research of the same subject were provided.

Development of Cuscuta species on a partially incompatible host: induction of xylem transfer cells.

The growth of dodders, Cuscuta reflexa and Cuscuta japonica, on the partially incompatible host poinsettia ( Euphorbia pulcherrima) is studied. Poinsettia responds by bark growths to the formation of the dodder haustoria and prevents dodder from obtaining normal growth. The growth instead becomes extremely branched, coral-like, and dodder lacks the ability to form haustoria. After a period of coral-like growth, long shoots sprout, resembling the normal growth. These long shoots mark an ending phase for dodder, which dies shortly after without having flowered. During the coral-like growth phase, dodder develops transfer cells in the parenchyma cells bordering the vessels of the xylem in the shoot. The transfer cells have not been observed when dodder is grown on the compatible host Pelargonium zonale. A coral-like growth phase has also been observed at the establishing phase when dodder is grown in vitro on agar; later a more normal growth form takes over. In this coral phase, xylem transfer cells are also developed. The fluorochromes carboxyfluorescein and Texas Red were loaded into the host in the phloem and xylem, respectively, and detection of these fluorochromes in the dodder stem indicated that a functional haustorial contact developed for both vascular systems. The results show that Cuscutaspp. have the genetic ability to develop xylem transfer cells and use this in response to developmental stress.

Dodder hyphae invade the host: a structural and immunocytochemical characterization.

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.