The desiccation-related proteins in Trebouxia: a family to discover

The transcriptome of Trebouxia gelatinosa, belonging to one of the most common genus of lichen photobionts, gave an interesting overview of the mechanisms that underlay the desiccation tolerance in this species, regarding structure, physiology and biochemistry. The analysis of the annotated transcripts of both the dehydrated and rehydrated cultured alga revealed interesting and peculiar features of this poikilohydric organism. In particular the presence of a large number of desiccation-related proteins (DRPs) was highlighted, most of them affected by at least one of the two treatments. The DRP family has been first described in the resurrection plants, then also in other plants and in green algae. In T. gelatinosa 13 sequences are classified as desiccation-related proteins. These identified sequences, clearly pertaining to the same multigenic family, are usually characterized by a c.170 a long ferritinlike domain (PF13668), followed by a C-terminal region of variable length without known annotated domains. Nine out of the 13 annotated transcripts were significantly responsive to dehydration and/or rehydration by either being up- or down-regulated. Because the number of DRP genes predicted in the analysed genomes of vascular plants is generally low - ranging from 0 to 5 - this gene family seems to have undergone an expansion in T. gelatinosa. Although the exact role of DRPs in the dehydration/rehydration processes is still unclear, their massive response, both in terms of gene number and fold change, to the hydric status of T. gelatinosa points out that they are prominent players in drought tolerance not only in resurrection plants but also in lichen photobionts. Our study aims at expanding the knowledge of the DRP family in rebouxia, in order to understand the role of these proteins and their expansion in desiccation tolerance and in relation to lichen symbiosis.