Musial, S. | bioRxiv Science

bioRxiv2024

A promiscuous mechanism to phase separate eukaryotic carbon fixation in the green lineage

CO2 fixation is commonly limited by inefficiency of the CO2-fixing enzyme Rubisco. Eukaryotic algae concentrate and fix CO2 in phase-separated condensates called pyrenoids, which complete up to one-third of global CO2 fixation. Condensation of Rubisco in pyrenoids is dependent on interaction with disordered linker proteins that show little conservation between species. We developed a sequence-independent bioinformatic pipeline to identify linker proteins in green algae. We report the linker from Chlorella and demonstrate that it binds a conserved site on the Rubisco large subunit. We show the Chlorella linker phase separates Chlamydomonas Rubisco and that despite their separation by [~]800 million years of evolution, the Chlorella linker can support the formation of a functional pyrenoid in Chlamydomonas. This cross-species reactivity extends to plants, with the Chlorella linker able to drive condensation of some native plant Rubiscos in vitro and in planta. Our results represent an exciting frontier for pyrenoid engineering in plants, which is modelled to increase crop yields.

plant biology↗

bioRxiv2023

Coordinated Chemokine Expression Defines Macrophage Subsets Across Tissues

Tissue-resident macrophages in the lung comprising alveolar and interstitial macrophages (IMs) display a high degree of heterogeneity. In general, macrophage heterogeneity is thought to arise from various forms of activation that are heavily confounded by the recruitment of monocytes to the tissue-resident macrophage pool. To better understand the functional heterogeneity of IMs in the lung, we profiled the transcription of resident CD206hi and CD206lo IMs under steady-state and inflammatory conditions, excluding recruited macrophages. Rather than observing conventional in vitro M1 and M2 activation states, we identified seven chemokine-expressing IM subsets: IMck1 (Ccl2, Ccl7, Ccl12, and some Cxcl14), IMck2-4 (Ccl3, Ccl4, Ccl5, Cxcl1, Cxcl2, and Cxcl3), IMck5 (Ccl8), IMck6 (Ccl6 and Ccl9), IMck7 (Cxcl9 and Cxcl10), IMck8 (Cxcl13), and IMck9 (Ccl24), which were found in steady-state or induced by acute inflammation. Beyond the mouse lung, similar coordinated chemokine signatures were observed in macrophages and monocytes from other tissues and across species. Although all IMs expressed Pf4 (CXCL4), mainly CD206hi IMs were selectively depleted in Pf4CreR26EYFP-DTR mice. Loss of CD206hi IMs resulted in significantly reduced inflammatory cell influx in allergen- and infection-driven models, as well as significantly diminished tertiary lymphoid formation and subsequent accumulation of GL7+ germinal center B cells. Overall, our study highlights a division of labor among interstitial macrophages, reflected by the coordinated production of chemokines to control inflammatory cell influx and organize tertiary lymphoid tissue architecture. One Sentence SummaryThe study highlights a division of labor among interstitial macrophages, reflected by the coordinated production of chemokines to control inflammatory cell influx and organize tertiary lymphoid tissue architecture.

immunology↗