Lichen rehydration in heavy metal-polluted environments: Pb modulates the oxidative response of both Ramalina farinacea thalli and its isolated microalgae.

Lichens are adapted to desiccation/rehydration and accumulate heavy metals, which induce ROS especially from the photobiont photosynthetic pigments. Although their mechanisms of abiotic stress tolerance are still to be unravelled, they seem related to symbionts' reciprocal upregulation of antioxidant systems. With the aim to study the effect of Pb on oxidative status during rehydration, the kinetics of intracellular ROS, lipid peroxidation and chlorophyll autofluorescence of whole Ramalina farinacea thalli and its isolated microalgae (Trebouxia TR1 and T. TR9) was recorded. A genetic characterization of the microalgae present in the thalli used was also carried out in order to assess possible correlations among the relative abundance of each phycobiont, their individual physiological responses and that of the entire thallus. Unexpectedly, Pb decreased ROS and lipid peroxidation in thalli and its phycobionts, associated with a lower chlorophyll autofluorescence. Each phycobiont showed a particular pattern, but the oxidative response of the thallus paralleled the TR1's, agreeing with the genetic identification of this strain as the predominant phycobiont. We conclude that: (1) the lichen oxidative behaviour seems to be modulated by the predominant phycobiont and (2) Pb evokes in R. farinacea and its phycobionts strong mechanisms to neutralize its own oxidant effects along with those of rehydration.

A single primer pair gives a specific ortholog amplicon in a wide range of Cyanobacteria and plastid-bearing organisms: applicability in inventory of reference material from collections and phylogenetic analysis.

The scarcity of universally applied molecular markers for algae has resulted in the development of multiple, independent and not easily comparable systems. The goal of this work is to increase the number of available molecular markers and to generate easily comparable systems. Thereby, we have designed a primer pair capable of amplifying a broad range of organisms: Cyanobacteria, Chlorophyta, Chlorarachniophyta, Cryptophyta, Euglenida, Glaucophyta, Rhodophyta, Stramenopiles and Streptophyta including plants. This primer pair can amplify a portion of the 23S rRNA gene with sufficient variability to identify reference material form collections across a broad range of taxa and perform phylogenetic studies alongside other available markers.

Suitability of chloroplast LSU rDNA and its diverse group I introns for species recognition and phylogenetic analyses of lichen-forming Trebouxia algae.

To date, species identification of lichen photobionts has been performed principally on the basis of microscopic examinations and molecular data from nuclear-encoded genes. In plants, the chloroplast genome has been more readily exploited than the nuclear genome for systematic investigations. At the present time, very little information is available about the chloroplast genome of lichen-forming algae. For this reason, we have sequenced a portion of the gene encoding for the chloroplast large sub-unit rRNA (LSU rDNA) as a new molecular marker. Sequencing of the chloroplast LSU rDNAs revealed the existence of an unusual diversity of group I introns (a total of 31) within 15 analyzed Trebouxia species. The number, sequence and insertion site of these introns were very different among species, contributing to their recognition. A relatively large intron-free portion of the chloroplast LSU rDNA and part of the nuclear ribosomal cistron (18S-5.8S-26S) between the nuclear internal transcribed spacers (nrITS) were subjected to phylogenetic analyses. The obtained results indicate that data combination from both nuclear and chloroplast sequences can improve phylogenetic accuracy. Herein, we propose the suitability of both intronic and exonic sequences of the chloroplast LSU rDNA for species recognition, and an exonic sequence spanning from position 879 to 1837 in the Escherichia coli 23S rDNA for phylogenetic analyses of Trebouxia phycobionts.

Primary transcripts of ndhD of Liliaceae and Aloaceae require editing of the start and 20th codons.

About 350 nucleotide sequences around the start codon of the plastid ndhD gene were determined in six species to investigate the requirement of C to U editing of the cryptic start codons. The comparison with other sequences in databanks showed that, in contrast to grasses and similarly to dicots, Liliaceae and Aloaceae require editing of the primary transcript to generate the AUG start codon. Primary transcripts of Liliaceae and Aloaceae also show a new editing site at the 59th nucleotide, which has not been described in other plants. In some cases, transcripts showed partial editing which suggests that the synthesis of the protein may be controlled at the level of transcript processing.

Transcripts of the ndhH-D operon of barley plastids: possible role of unedited site III in splicing of the ndhA intron.

The plastid ndhH-D operon produces several transcripts containing ndhA sequence with and without its group II intron. After sequencing an 8125 bp fragment of barley plastid DNA including the ndhH-D operon, we investigated the editing-splicing status of transcripts in the range 1.0-7.8 kb. Reverse transcription and sequencing of RNA bands separated by electrophoresis were used to determine C-->U editing sites. Sites I, II and IV of ndhA and site V of ndhD were edited in all transcripts analysed and, probably, were edited before any splicing had taken place. In contrast, site III of ndhA (13 bp from the 5'-end base of the second exon) was not edited in transcripts containing the intron (including the 1.7 kb intermediary transcript consisting of the intron and the second exon) but was edited in all transcripts lacking the ndhA intron. Comparison of the secondary structures of the ndhA intron and intron-second exon intermediate suggests that G pairing prevents editing of site III in transcripts containing the intron and maintains the secondary structure required for splicing. Splicing of the ndhA intron releases the site III C from pairing and, probably, brings it close to cis-acting elements for editing upstream in the first exon.