Current Science

Singh Shweta ¹, B. R. Gurumurthy ², M. M. Vasanthakumari ¹, G. Ravikanth ³, S. Dayanandan ⁴, R. Storms ⁴, M. B. Shivanna ⁵, R. Uma Shaanker ¹

Affiliations
1 School of Ecology and Conservation and Department of Crop Physiology, University of Agricultural Sciences, GKVK, Bengaluru 560 065, IN
2 Department of Crop Physiology, University of Agricultural and Horticultural Sciences, Shivamogga 577 201, IN
3 Ashoka Trust for Research in Ecology and the Environment, Royal Enclave, Srirampura, Jakkur PO, Bengaluru 560 064, IN
4 Centre for Structural and Functional Genomics and Biology Department, Concordia University, 7141 Sherbrooke West, Montreal, Quebec, H4B 1R6, CA
5 Department of Applied Botany, Kuvempu University, Jnana Sahyadri, Shankaraghatta, Shivamogga 577 451, IN

Abstract

Nothapodytes nimmoniana Graham (Icacinaceae) is a small tree distributed along a 1600 km mountain range in the Western Ghats biodiversity hotspot in southern India. The stem wood of N. nimmoniana accumulates high concentration (about 0.3% by dry weight) of the anti-cancer alkaloid, camptothecine (CPT). Several endophytic fungi isolated from this plant have been shown to produce camptothecine in vitro. In this study, we examined the diversity and distribution of fungal endophytes of N. nimmoniana along its entire distributional range in the Western Ghats and investigated if the CPT-producing endophytes are restricted to any specific clade. The leaf and stem of N. nimmoniana were sampled from 18 sites along the Western Ghats spanning 8-18°N lat. Endophytes were recovered from all sites with the colonization frequency ranging from 0% to 52% across the sites. One hundred and four endo-phytic fungal isolates were recovered from 118 plants and characterized both morphologically and by sequencing the internally transcribed spacer region of the nuclear rDNA gene. The fungal isolates belonged to 45 species (44 Ascomycetes and one Basidiomycetes). Fusarium and Hypoxylon were the most predominant genera comprising over half of the total isolates. Interestingly, CPT-producing endophytes were not restricted to any specific clade. We discuss these results in the context of the growing interest in endophytic fungi as possible alternative sources of plant secondary metabolites.

Keywords

Camptothecine, Endophytic Fungi, Fungal Diversity and Distribution, Nothapodytes nimmoniana.

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S. Shweta ¹, M. B. Shivanna ², B. R. Gurumurthy ³, R. Uma Shaanker ¹, T. R. Santhosh Kumar ⁴, G. Ravikanth ⁵

Affiliations
1 School of Ecology and Conservation and Department of Crop Physiology, University of Agricultural Sciences, GKVK, Bangalore 560 065, IN
2 Kuvempu University, Jnana Sahyadri, Shankaraghatta, Shimoga 577 451, IN
3 University of Agriculture and Horticulture Sciences, Shimoga 577 204, IN
4 Apoptosis and Cell Signalling, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram 695 014, IN
5 Ashoka Trust for Research in Ecology and the Environment, Royal Enclave, Srirampura, Jakkur PO, Bangalore 560 064, IN

Abstract

Camptothecine (CPT), a monoterpene indole alkaloid, is a potent inhibitor of eukaryotic topoisomerase I. It is produced by a number of plants, including Notha-podytes nimmoniana (Grahm) Mabb. (Icacinaceae), occurring naturally in the Western Ghats, India. The plant is inhabited by a number of endophytic fungi, many of which have been isolated and shown to pro-duce CPT, in culture, independent of the host. In this article, we examine the sensitivity of endophytic fungi isolated from N. nimmoniana to CPT. Contrary to our hypothesis that these fungi should be resistant to CPT (as they are exposed to host CPT as well as that pro-duced by themselves), we report that these fungi are sensitive and thus inhibited by CPT. We discuss these results in the context of the role of CPT in limiting endophytic fungal growth.

Keywords

Camptothecine, Endophytic Fungi, Nothapo-dytes nimmoniana, Sensitivity and Inhibition.

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