Ever since plants colonized land,they evolved mechanisms to respond to changing environmental conditions and settle in extreme habitats.Recent studies show that several plant species require microbial associations for stress tolerance and survival.Although many plants lack the adaptive capability to adapt to stress conditions,the ability of a variety of plants to adapt to stress conditions often appears to depend on their association with certain microbes,raising a number of questions:What distinguishes the microbes and plants that can adapt to extreme environmental conditions? Can all plants improve stress tolerance when associated with appropriate microbial partners? Answers to these questions should modify our concepts of plant physiology and could lead to new ways towards a sustainable agriculture.