Gesneriads, a Source of Resurrection and Double-Tolerant Species: Proposal of New Desiccation- and Freezing-Tolerant Plants and Their Physiological Adaptations

SIMPLE SUMMARY: In the current scenario of climate change, plants need to overcome a great amplitude of temperatures and increasingly common droughts in the very same space. Gesneriads are a worldwide family of plants in which many “resurrection” species have arisen: plants with the ability to withstand long periods of time with very little water content and successfully revive upon water availability. Due to their rocky and mountainous habitat, many of them have to face a great temperature variability and freezing temperatures, and indeed, their resurrection ability and freezing tolerance share similar metabolic responses. Tolerance of gesneriads to different environmental stresses is thought to be applicable in crop growth improvement, but their difficult indoor cultivation and outdoor accessibility are major obstacles for their study. Therefore, this review aims to identify common patterns in the already known resurrection species to propose new tentative resurrection gesneriads, as well as gather the metabolic responses to desiccation and freezing stress as a way of making them more reachable to the scientific community. ABSTRACT: Gesneriaceae is a pantropical family of plants that, thanks to their lithophytic and epiphytic growth forms, have developed different strategies for overcoming water scarcity. Desiccation tolerance or “resurrection” ability is one of them: a rare phenomenon among angiosperms that involves surviving with very little relative water content in their tissues until water is again available. Physiological responses of desiccation tolerance are also activated during freezing temperatures, a stress that many of the resurrection gesneriads suffer due to their mountainous habitat. Therefore, research on desiccation- and freezing-tolerant gesneriads is a great opportunity for crop improvement, and some of them have become reference resurrection angiosperms (Dorcoceras hygrometrica, Haberlea rhodopensis and Ramonda myconi). However, their difficult indoor cultivation and outdoor accessibility are major obstacles for their study. Therefore, this review aims to identify phylogenetic, geoclimatic, habitat, and morphological features in order to propose new tentative resurrection gesneriads as a way of making them more reachable to the scientific community. Additionally, shared and species-specific physiological responses to desiccation and freezing stress have been gathered as a stress response metabolic basis of the family.