Lindernia brevidens:: a novel desiccation-tolerant vascular plant, endemic to ancient tropical rainforests

A particular adaptation to survival under limited water availability has been realized in the desiccation-tolerant resurrection plants, which tend to grow in a habitat with seasonal rainfall and long dry periods. One of the best-studied examples is Craterostigma plantagineum. Here we report an unexpected finding: Lindernia brevidens, a close relative of C. plantagineum, exhibits desiccation tolerance, even though it is endemic to the montane rainforests of Tanzania and Kenya, where it never experiences seasonal dry periods. L. brevidens has been found exclusively in two fragments of the ancient Eastern Arc Mountains, which were protected from the devastating Pleistocene droughts by the stable Indian Ocean temperature. Analysis of the microhabitat reveals that L. brevidens is found in the same habitat as hygrophilous plant species, which further indicates that the plant never dries out completely. The objective of this investigation was to address whether C. plantagineum and L. brevidens have desiccation-related pathways in common, or whether L. brevidens has acquired novel pathways. A third, closely related, desiccation-sensitive species, Lindernia subracemosa, has been included for comparison. Mechanisms that confer cellular protection during extreme water loss are well conserved between C. plantagineum and L. brevidens, including the interconversion of 2-octulose to sucrose within the two desiccation-tolerant species. Furthermore, transcriptional control regions of desiccation-related genes belonging to the late embryogenesis abundant (LEA) protein family are also highly conserved. We propose that L. brevidens is a neoendemic species that has retained desiccation tolerance through genome stability, despite tolerance being superfluous to environmental conditions.