New features of desiccation tolerance in the lichen photobiont Trebouxia gelatinosa are revealed by a transcriptomic approach

Abstract

Trebouxia is the most common lichen-forming genus of aero-terrestrial green algae and all its species are desiccation tolerant (DT). The molecular bases of this remarkable adaptation are, however, still largely unknown. We applied a transcriptomic approach to a common member of the genus, T. gelatinosa, to investigate the alteration of gene expression occurring after dehydration and subsequent rehydration in comparison to cells kept constantly hydrated. We sequenced, de novo assembled and annotated the transcriptome of axenically cultured T. gelatinosa by using Illumina sequencing technology. We tracked the expression profiles of over 13,000 protein-coding transcripts. During the dehydration/rehydration cycle c. 92 % of the total protein-coding transcripts displayed a stable expression, suggesting that the desiccation tolerance of T. gelatinosa mostly relies on constitutive mechanisms. Dehydration and rehydration affected mainly the gene expression for components of the photosynthetic apparatus, the ROS-scavenging system, Heat Shock Proteins, aquaporins, expansins, and desiccation related proteins (DRPs), which are highly diversified in T. gelatinosa, whereas Late Embryogenesis Abundant Proteins were not affected. Only some of these phenomena were previously observed in other DT green algae, bryophytes and resurrection plants, other traits being distinctive of T. gelatinosa, and perhaps related to its symbiotic lifestyle. Finally, the phylogenetic inference extended to DRPs of other chlorophytes, embryophytes and bacteria clearly pointed out that DRPs of chlorophytes are not orthologous to those of embryophytes: some of them were likely acquired through horizontal gene transfer from extremophile bacteria which live in symbiosis within the lichen thallus.

The purplish bifurcate mussel Mytilisepta virgata gene expression atlas reveals a remarkable tissue functional specialization

“…The minimum contig length was set at 200 bp. As suggested by previous studies [25, 26], in order to remove unreliable sequences likely originated from excessive fragmentation of longer mRNA molecules or residual contamination from exogenous RNA, contigs displaying a very low sequencing coverage were removed; this procedure was based on a threshold of TPM = 1, calculated with the back-mapping of all trimmed reads on the full assembled transcriptome using the software Kallisto v0.43.0 [27]. All the contigs that did not reach this threshold were discarded.…”

Seed desiccation mechanisms co‐opted for vegetative desiccation in the resurrection grass Oropetium thomaeum

“…Transcriptional and metabolic changes during desiccation in Oropetium mirror patterns observed in other angiosperm resurrection plants including the eudicots Boea hygrometrica (Xiao et al 2015), C. plantagineu (Rodriguez et al 2010) and monocots Sporobolus (Yobi et al 2017), Xerophyta (Costa et al 2017) and Tripogon (Williams et al 2015) among others. Similar patterns are also observed in the mosses Tortula ruralis (Oliver et al 2009) and Bryum argenteum (Gao et al 2015) and the streptophyte green alga Klebsormidium (Holzinger et al 2014) and terrestrial algae Trebouxia gelatinosa (Carniel et al 2016). This suggests a similar transcriptional machinery is activated across land plants and algae, supporting a shared origin of this trait.…”

“…) and terrestrial algae Trebouxia gelatinosa (Carniel et al . ). This suggests a similar transcriptional machinery is activated across land plants and algae, supporting a shared origin of this trait.…”

Transcriptomic Profiling Reveals Metabolic and Regulatory Pathways in the Desiccation Tolerance of Mungbean (Vigna radiata [L.] R. Wilczek)

“…HSPs are responsible for protein folding, and can assist in protein refolding under stress conditions (Wu et al, 2015; Carniel et al, 2016; Wang et al, 2016). Overexpression of the HaHSFA9 and HaHSFA4a in tobacco demonstrated their roles in DT (Almoguera et al, 2015).…”