RESUMO
Pyrocystis lunula is a unicellular bioluminescing dinoflagellates. While the mechanisms and genes underlying bioluminescence and luciferase synthesis are understood in many bioluminescing clades, it remains unknown in dinoflagellates. We took advantage of merging long and short reads to provide here a de novo assembly of P. lunula transcriptome. A total of 975 million filtered paired-end reads were obtained and assembled into 155,716 contigs corresponding to putative transcripts that were functionally annotated. This dataset will be valuable for improving our understanding of protist's biology and is accessible via NCBI BioProject (PRJNA727555).
RESUMO
Chlorophyll (Chl) breakdown is a diagnostic visual process of leaf senescence, which furnishes phyllobilins (PBs) by the PAO/phyllobilin pathway. As Chl breakdown disables photosynthesis, it appears to have no role in photoactive green leaves. Here, colorless PBs were detected in green, non-senescent leaves of Arabidopsis thaliana. The PBs from the green leaves had structures entirely consistent with the PAO/phyllobilin pathway and the mutation of a single Chl catabolic enzyme completely abolished PBs with the particular modification. Hence, the PAO/phyllobilin pathway was active in the absence of visible senescence and expression of genes encoding Chl catabolic enzymes was observed in green Arabidopsis leaves. PBs accumulated to only sub-% amounts compared to the Chls present in the green leaves, excluding a substantial contribution of Chl breakdown from rapid Chl turnover associated with photosystem II repair. Indeed, Chl turnover was shown to involve a Chl a dephytylation and Chl a reconstitution cycle. However, non-recyclable pheophytin a is also liberated in the course of photosystem II repair, and is proposed here to be scavenged and degraded to the observed PBs. Hence, a cryptic form of the established pathway of Chl breakdown is indicated to play a constitutive role in photoactive leaves.
