The mutualistic symbiont Piriformospora indica exhibits a great potential in agriculture. The interaction between P. indica and Chinese cabbage (Brassica campestris cv. Chinensis) results in growth and biomass promotion of the host plant and in particular in root hair development. The resulting highly bushy root phenotype of colonized Chinese cabbage seedlings differs substantially from reports of other plant species, which prompted the more detailed study of this symbiosis. A large-scale expressed sequence tag (EST) data set was obtained from a double-subtractive EST library, by subtracting the cDNAs of Chinese cabbage root tissue and of P. indica mycelium from those of P. indica-colonized root tissue. The analysis revealed ~700 unique genes rooted in 141 clusters and 559 singles. A total of 66% of the sequences could be annotated in the NCBI GenBank. Genes which are stimulated by P. indica are involved in various types of transport, carbohydrate metabolism, auxin signalling, cell wall metabolism, and root development, including the root hair-forming phosphoinositide phosphatase 4. For 20 key genes, induction by fungal colonization was confirmed kinetically during the interaction by real-time reverse transcription–PCR. Moreover, the auxin concentration increases transiently after exposure of the roots to P. indica. Microscopic analyses demonstrated that the development of the root maturation zone is the major target of P. indica in Chinese cabbage. Taken together, the symbiotic interaction between Chinese cabbage and P. indica is a novel model to study root growth promotion which, in turn, is important for agriculture and plant biotechnology.
Human endogenous retroviruses (HERVs), abundantly inter-dispersed in the genome, carry long terminal repeats (LTRs) that may potentially retro-transpose to new genomic sites and deregulate the neighboring cellular genes. However, normally HERVs are either structurally defective or inactive due possibly to stringent negative control mechanisms. To study the possible negative regulation of HERV, we isolated the LTR of RTVL-Ia and constructed site-specific mutations for analysis of the promoter and enhancer functions by using chloramphenicol acetyl transferase (CAT) reporter assay. Our results showed that in most transfected human cells the LTR-mediated CAT expression was negligible unless a sequence segment at the AGTAAA polyadenylation site was deleted. In addition, we have found that the wild type p53 may inhibit whereas a p53 mutant (V143A) stimulate the transcriptional activity of HERV-I LTR. Our results imply that HERV-I LTR, while under negative control by its LTR cis-elements and by wild type p53, may become active upon p53 mutation.
Piriformospora indica, an endophytic fungus of Sebacinales, has a wide host range and promotes the performance of mono-and eudicot plants. Here, we compare the interaction of P. indica with the roots of seven host plants (Anthurium andraeanum, Arabidopsis thaliana, Brassica campestris, Lycopersicon esculentum, Oncidium orchid, Oryza sativa, and Zea mays). Microscopical analyses showed that the colonization time and the mode of hyphal invasion into the roots differ in the symbiotic interactions. Substantial differences between the species were also observed for the levels and accumulation of jasmonate (JA) and gibberellin (GA) and the transcript levels for genes involved in their syntheses. No obvious correlation could be detected between the endogenous JA and/or GA levels and the time point of root colonization in a given plant species. Our results suggest that root colonization strategies and changes in the two phytohormone levels are highly host-specific.
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