Contents lists available at ScienceDirect Applied Soil Ecology journal homepage: www.elsevier.com/locate/apsoil Effect of Thermomyces fungal endophyte isolated from extreme hot desert- adapted plant on heat stress tolerance of cucumber Abeer H. Ali a , Mostafa Abdelrahman a,b, ⁎ , Usama Radwan a , Soad El-Zayat a , Magdi A. El-Sayed a,c, ⁎ a Botany Department, Faculty of Sciences, Aswan University, Aswan 81528, Egypt b Graduate School of Life Sciences, Tohoku University, Sendai 9808577, Japan c Unit of Environmental Studies and Development, Aswan University, Aswan 81528, Egypt ARTICLE INFO Keywords: Plant-endophytes association Heat stress Photosynthesis Antioxidant ABSTRACT With the increasing effects of global climate change and population growth, there is a high need for new agricultural practices to maximize efficiencies and reduce the efforts needed for developing new crop varieties that can withstand various abiotic stress. Plant-microbe association to optimize plant growth and increase plant host stress tolerance may play an essential role in improving environmental sustainability and economic via- bility, especially in the arid land habitats. In the present study, photosynthetic responsiveness was selected to demonstrate that a theromophilic endophytic (CpE) fungus isolated from the hot desert-adapted delile (Cullen plicata) roots can mediate heat stress tolerance in cucumber plants grown in the field during the summer season in Egypt. Initially, the CpE isolate was identified using an internal transcribed spacer, revealing 92% sequence homology with Thermomyces sp. Then the cucumber seeds were treated with CpE endophyte spore and allowed to grow in a growth chamber for three weeks before transplanting into the field station from May to July. The CpE treatment eliminates the adverse effects of heat stress on cucumber plants by maintaining the maximum quantum efficiency of photosystem II, photosynthesis rate, water use efficiency and increase root length relative to untreated plants. In addition, CpE treatments induced the significant accumulation of total sugars, flavonoids, saponins, soluble proteins and antioxidant enzyme activities in comparison with untreated cucumber plants. Our finding provides novel insights into the eco-physiological mechanisms of thermophilic CpE-mediated heat stress tolerance in cucumber, which signify the prospective applications of arid land-adapted endophytes in agri- cultural systems. 1. Introduction Impacts from recent climate-related conditions, such as heat-waves and persistent drought in addition to the reductions in the quantity and quality of arable land and water will change the current and future world agricultural production (Abdelrahman et al., 2017a, 2017b). Heat waves are predicted to become more frequent and persistent more prolonged than what is being currently observed in recent years, especially during the summer season, affecting ecosystem productivity and diversity (Hatfield and Prueger, 2015). Despite these encounters, global food production will have to rise by 70% to meet the mandate of an anticipated increase in population growth to 9 billion by 2050 (Stratonovitch and Semenov, 2015; Abdelrahman et al., 2017b), which will push agriculture sustainability to the edges in the coming years. To meet these challenges, new discoveries and research technologies aim to maximize efficiencies and reduce the inputs needed for developing new crop varieties and maintain water usage will be essential to improve agriculture sustainability and food security. Traditional breeding programs to develop abiotic stress-resilient crops remain in- sufficient due to the lack of abiotic stress resistance germplasms and time-consuming (Zhang, 2016). Recently, the association between the plant and the extreme habitat-adapted endophytes or beneficial mi- croorganisms is becoming a well-established strategy to enhance plant survival capacity and increase yield under various abiotic and biotic stresses (Khan et al., 2012; Jogaiah et al., 2013; Abdelrahman et al., 2016; Gill et al., 2016; Khan et al., 2016). The genetic base of abiotic stress resistance in extremophilic fungi, particularly thermophilic one is a unique genetic resource, enabling the plant to survive under abiotic stress conditions (Zhang, 2016). For example, Thermomyces sp. is a thermophilic fungus that can survive at 62 °C due to the presence of ubiquitin degradation, histone acetylation/deacetylation, and poly ADP-ribosylation pathways, which play a crucial role in Thermomyces response to heat stress (Mchunu et al., 2013). However, the beneficial role of this thermophilic fungi to induce heat stress tolerance in crop https://doi.org/10.1016/j.apsoil.2017.11.004 Received 27 September 2017; Received in revised form 1 November 2017; Accepted 3 November 2017 ⁎ Corresponding authors at: Botany Department, Faculty of Sciences, Aswan University, Aswan 81528, Egypt. E-mail addresses: meettoo2000@ige.tohoku.ac.jp (M. Abdelrahman), magdiel_sayed@aswu.edu.eg (M.A. El-Sayed). Applied Soil Ecology xxx (xxxx) xxx–xxx 0929-1393/ © 2017 Elsevier B.V. All rights reserved. Please cite this article as: Ali, A.H., Applied Soil Ecology (2017), http://dx.doi.org/10.1016/j.apsoil.2017.11.004