genetic regulation of cross tolerance in plants under biotic and abiotic stresses

plants face many biotic and abiotic stresses at the same time during their growth under field conditions. plants responses toward combined stresses are often more complex than their responses to one type of stress in a way that the results of these responses are called as cross tolerance. this mixture of stresses activates specific models of gene expression that causes special signaling networks and activation of some components of resistance reactions in plants like systemic acquired resistance and r-genes. recently, because of great progresses in genetic sciences, genetic regulation of cross tolerance has gained a lot of attention and it seems that genome reprogramming influenced by combined stresses can play a special role through inducing defense responses in plants. depending on the nature, duration, and intensity of stresses, their impacts on plants can be additive or antagonistic. actually, a range of molecular mechanisms are activated in order to respond to a new situation. the components of these mechanisms include reactive oxygen species, hormone signaling and transcription factors. nowadays, a great challenge in plant cross tolerance is how plants balance their resources between growth and defence against stresses. this review focuses on the responses of plants to simultaneous biotic and abiotic stresses at the molecular level and the importance of studying plant stress factors in combination.