Biology subjects

Schmid-Siegert, E.

Publications and source records attributed to Schmid-Siegert, E..

3 recordsLinked to original sources

bioRxiv2018

PIF transcription factors link a neighbor threat cue to accelerated reproduction in Arabidopsis

Changes in light quality indicative of competition for this essential resource influence plant growth and developmental transitions. Little is known about neighbor proximity-induced acceleration of reproduction. phytochrome B (phyB) senses light cues from plant competitors ultimately leading to the expression of the floral inducers FLOWERING LOCUS (FT) and TWIN SISTER of FT (TSF). Here we show that three PHYTOCHROME INTERACTING FACTOR (PIF) transcriptional regulators act directly downstream of phyB to promote expression of FT and TSF. Neighbor proximity enhances PIF accumulation towards the end of the day coinciding with enhanced floral inducer expression. We present evidence for direct PIF-mediated TSF expression. The relevance of our findings is illustrated by the prior identification of FT, TSF and PIF4 as loci underlying flowering time regulation in nature.\n\nOne Sentence SummaryPIF transcription factors mediate reproductive transition in response to neighbor proximity light cues in Arabidopsis.

plant biology↗

bioRxiv2017

Mechanisms of surface antigenic variation in the human pathogenic fungus Pneumocystis jirovecii

Microbial pathogens commonly escape the human immune system by varying surface proteins. We investigated the mechanisms used for that purpose by Pneumocystis jirovecii. This uncultivable fungus is an obligate pulmonary pathogen which causes pneumonia in immuno-compromised individuals, a major life-threatening infection. Long-read PacBio sequencing was used to assemble a core of subtelomeres of a single P. jirovecii strain from a bronchoalveolar lavage fluid specimen of a single patient. A total of 113 genes encoding surface proteins were identified, including 28 pseudogenes. These genes formed a subtelomeric gene superfamily which included five families encoding adhesive GPI-anchored glycoproteins, and one family encoding excreted glycoproteins. Numerical analyses suggested that diversification of the glycoproteins relies on mosaic genes created by ectopic recombination, and occurs only within each family. DNA motifs suggested that all genes are expressed independently, except those of the family encoding the most abundant surface glycoproteins which are subject to mutually exclusive expression. PCR analyses showed that exchange of the expressed gene of the latter family occurs frequently, possibly favoured by the location of the genes proximal to the telomere because this allows concomitant telomere exchange. Our observations suggest that (i) P. jirovecii cell surface is made of a complex mixture of different surface proteins, with a majority of a single isoform of the most abundant glycoprotein, (ii) genetic mosaicism within each family ensures variation of the glycoproteins, and (iii) the strategy of the fungus consists in the continuous production of new subpopulations composed of cells which are antigenically different.

microbiology↗

bioRxiv2017

Low Rate of Somatic Mutations in a Long-Lived Oak Tree

Because plants do not possess a proper germline, deleterious somatic mutations can be passed to gametes and a large number of cell divisions separating zygote from gamete formation in long-lived plants may lead to many mutations. We sequenced the genome of two terminal branches of a 234-year-old oak tree and found few fixed somatic single-nucleotide variants (SNVs), whose sequential appearance in the tree could be traced along nested sectors of younger branches. Our data suggest that stem cells of shoot meristems are robustly protected from accumulation of mutations in trees.

plant biology↗