Biology subjects

Sittmann, J.

Publications and source records attributed to Sittmann, J..

3 recordsLinked to original sources

bioRxiv2026

Molecular underpinning of Hydra viridissima-algal facultative symbiosis and vertical algal transmission

The symbiosis between algae and animals represents a relatively recent evolutionary innovation, and exemplified by species in the Cnidaria phylum. Cnidaria can harbor algae within a modified cellular organelle called the symbiosome in a process called endosymbiosis. This animal-algal symbiosis can be facultative or obligate. Algae acquisition occurs either by horizontal transmission, where free-swimming planula gain algae through feeding, or by algae deposition into the developing oocyte in vertical transmission[1-5]. Most studies focus on anthozoans that perform obligate endosymbiosis and transmit algae horizontally. How facultative endosymbiosis in combination with vertical algal transmission impacts the evolutionary adaptation between host and symbiont remains unclear. By studying Hydra viridissima, which performs facultative endosymbiosis and transmits its Chlorella algae vertically, we define different cell types and identify the endoderm cell lineage that gives rise to three major cell types hosting algae. Compared to obligate endosymbiosis[6, 7], Hydra viridissima algal host cells exhibit distinct features, including algal uptake, elevated oxidative phosphorylation and redox activities, and express genes that can provide ammonium for their algal symbionts. We further show when and how the developing Hydra oocytes may take up algae and where oocytes may obtain lipids. Since Hydra is amenable to genetic manipulations, our findings should enable mechanistic studies of how facultative endosymbiosis and vertical transmission evolve and adapt in a changing climate.

molecular biology↗

bioRxiv2020

Bacterially produced small molecules stimulate diatom growth

Diatoms are photosynthetic microalgae that fix a significant fraction of the worlds carbon. Because of their photosynthetic efficiency and high-lipid content, diatoms are priority candidates for biofuel production. Here, we report that sporulating Bacillus thuringiensis when in co-culture with a marine diatom Phaeodactylum tricornutum significantly increases the diatom cell count. Bioassay-guided purification led to the identification of two diketopiperazines (DKPs) that both stimulate P. tricornutum growth and increase its lipid content. RNA-seq analysis revealed upregulation of a small set of P. tricornutum genes involved in iron starvation response and nutrient recycling when DKP was added to the diatom culture. This work demonstrates that two DKPs produced by a bacterium could positively impact P. tricornutum growth and lipid content, offering new approaches to enhance P. tricornutum-based biofuel production. As increasing numbers of DKPs are isolated from marine microbes, the work gives potential clues to bacterially produced growth factors for marine microalgae. One sentence summaryTwo diketopiperazines (DKPs) produced by sporulating bacterium Bacillus thuringiensis stimulate diatom P. tricornutum growth and increase diatom lipid content.

plant biology↗

bioRxiv2020

Mechanism of auxin and GA crosstalk in diploid strawberry fruit initiation

Strawberry, a high value fruit crop, has recently become amenable for genetic studies due to genomic resources and CRISPR/CAS9 tools. Unlike ovary-derived botanical fruits, strawberry is an accessory fruit derived from receptacle, the stem tip subtending floral organs. Although both botanical and accessory fruits initiate development in response to auxin and GA released from seeds, the downstream auxin and GA signaling mechanisms underlying accessory fruit development remain unknown. Using wild strawberry, we performed in depth molecular characterizations of accessory fruit development. We show that auxin signaling proteins FveARF8/FveARF6 are bound and hence inhibited by FveIAA4 and FveRGA1, repressors in auxin and GA signaling pathways. This inhibition is relieved post-fertilization or by the application of GA or auxin. Mutants of FveRGA1 developed parthenocarpic fruit suggesting a conserved function of DELLA proteins in fruit set. Further, FveARF8 was found to repress the expression of a GA receptor gene GID1c to control fruits sensitivity to GA, revealing a novel crosstalk mechanism. We demonstrate that consensus co-expression network provides a powerful tool for non-model species in the selection of interacting genes for functional studies. These findings will facilitate the improvement of strawberry fruit productivity and quality by guiding future production of parthenocarpic fruit. One sentence summaryGenome editing and network analysis are applied to investigating the mechanism of accessory fruit initiation in the wild strawberry, revealing conserved as well as novel crosstalk mechanisms. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantcell.org) is: Zhongchi Liu (zliu@umd.edu)

plant biology↗