Thermotolerance of fungal endophytes isolated from plants adapted to the Thar Desert, India

A total of 507 endophytic fungal isolates belonging to 82 operational taxonomic units (OTUs) were isolated from fifteen plant species naturally occurring in the Thar Desert, Rajasthan, India. Aspergillus, Alternaria, Chaetomium, Penicillium and Nigrospora were among the dominant fungal genera. Thermotolerance of the isolates was evaluated by culturing the fungi at 40 °C and 45 °C in shake flasks. Growth of nine OTUs (ACJ-2, ACJ-5, ACL-2, ACT-2, ACT-3, LAS-4, LAS-6, SAP-3 and SAP-6) was unaffected at 40 °C. Of these, six endophytes, namely, ACJ-2, ACJ-5 (Aspergillus flavus), SAP-3 (Aspergillus sp.), SAP-6, LAS-4 (Aspergillus sp.) and LAS-6 (Chaetomium sp.), were tolerant to as high as 45 °C. Rest of the OTUs did not survive culture temperatures beyond 35 °C. We evaluated the ability of one thermotolerant endophyte, LAS-6 (Chaetomium sp.) to confer high temperature tolerance and three OTUs, namely, LAS-4 (Aspergillus sp.), SAP-3 (Aspergillus sp.) and SAP-6 to confer drought tolerance to a rice cultivar, IR-64, at early seedling stage. Seedlings treated with LAS-6 (Chaetomium sp.) showed a higher survival percentage as well as maintained a significantly higher shoot and root growth under high temperature stress compared to seedlings not treated with the fungus. Under drought stress, endophyte treated seedlings maintained a significantly higher root growth compared to untreated seedlings. The identified thermotolerant fungal sources could be potentially useful in alleviating abiotic stress in agriculturally important crops

Role of endophytes in early seedling growth of plants: a test using systemic fungicide seed treatment

Systemic fungicide seed treatments are routinely used in conventional agriculture to control soil and seedborne diseases, but little is known about their unintended adverse effects on non-target beneficial fungal endophytes that are known to be involved in plant growth and development. This study evaluated the seed treatment effect of a broad spectrum systemic fungicide, carbendazim (bavistin) on symbiotic association of fungal endophytes in rice and on early seedling growth of rice, green gram, soybean, and cowpea. Seeds were surface sterilized with sodium hypochlorite followed by 0.2% bavistin treatment. Growth of fungal endophytes was significantly affected by the seed treatment with fungicide in rice seedlings, while shoot and root growth was suppressed in all the crops. Quantitative real time PCR showed that the level of expression of two basal transcriptional regulator genes, OsBTF3 and OsNFYC1 that are required for seed germination and seedling growth significantly decreased in bavistin treated rice seedlings. Re-inoculation of consortia of fungal endophytes onto bavistin treated rice seedlings significantly recovered seedling growth and development. These results suggest that fungicide treatment of seeds affects early seedling growth and has negative impact on beneficial fungal endophytes that are involved in plant growth and development. This study provides information on possible ill effects of fungicide on beneficial fungal endophytes that play key roles in early seedling growth of plants and also open up the prospect to additional research on different crops in vitro and field conditions to determine the consequences of fungicide effects and optimise fungicide application strategies to develop sustainable disease control methods

Endophytes and Plant Secondary Metabolite Synthesis: Molecular and Evolutionary Perspective

The distribution of endophytes (fungal and bacterial) is ubiquitous and almost without exception; the endophytes have been reported from all tissues, including leaves, stems, roots, flowers and fruits. As typical symptomless organisms, in contrast to their pathogenic counterparts, they pose a serious challenge in explaining their continued maintenance in plants. How do plants tolerate them? And how do the endophytes contain the plant defences? But a more intriguing and enigmatic issue with many endophytes is the fact that they mimic the production of specific plant associated secondary metabolites (e.g. taxol, camptothecin and rohitukine) in culture, independent of the host tissue. Several theories including the possibility of horizontal gene transfer from the respective hosts have been proposed, but none has so far been supported. In this paper, we critically review studies on endophytes producing plant secondary metabolites and explore the possible molecular mechanisms. By analysing the pathway genes for a few major metabolites, including taxol and camptothecin, we show that a far more intricate molecular mechanism might be involved in the production of the secondary metabolites by the endophytes. We show that these molecular mechanisms could have arisen through the evolutionary interactions of the endophytes with their respective host plants. We discuss these findings in the context of the current interest in harnessing endophytes as alternative sources of plant secondary metabolites