Meeda, Y. | Search bioRxiv

bioRxiv2025

A plasma membrane Ca2+-dependent protein kinase PtCDPK2 promotes phosphorus starvation resilience in Phaeodactylum tricornutum

Phosphorus (P) is an essential element limiting algal growth and productivity in aquatic ecosystems. Diatoms are important microalgae that thrive in nutrient-variable environments. Determining how diatoms perceive and respond to P availability is therefore crucial for understanding their ecological success. P-limited diatoms use a calcium (Ca2+)-dependent signalling pathway to sense and coordinate cellular responses to phosphate resupply. Despite the importance of Ca2+ signalling for diatom environmental sensing, apparatus enabling Ca2+ signal decoding is poorly understood. Here, we characterise the repertoire of an important group of Ca2+ sensor proteins--Ca2+ dependent protein kinases (CDPKs), in Phaeodactylum tricornutum. Several PtCDPKs are transcriptionally upregulated under P starvation. To determine whether PtCDPKs can coordinate P-starvation responses or act to transduce Ca2+ signals induced by P resupply, we functionally characterised PtCDPK2. PtCDPK2 is highly expressed in P-limited cells and localises to the cell periphery, suggesting a role regulating plasma membrane processes. Further, PtCDPK2 is co-regulated with the transcriptional regulator of P-starvation responses, PtPSR1. PtCDPK2 expression is also coordinated with the induction of P-Ca2+ signalling, which is driven by depletion of cellular P rather than external P exhaustion, or growth limitation. Ptcdpk2 mutants have significantly reduced photosynthetic efficiency and alkaline phosphatase activity under P starvation, but we do not find evidence for a direct role coordinating downstream responses to P resupply. These findings suggest PtCDPK2 is essential for regulating P-starvation physiology and reveals a role for Ca2+-signalling apparatus in promoting diatom tolerance in low P environments.

cell biology↗

bioRxiv2021

The unique neuronal structure and neuropeptide repertoire in the ctenophore Mnemiopsis leidyi shed light on the evolution of animal nervous systems

The ctenophore nerve net represents one of the earliest evolved nervous system of animals. Due to the uncertainties of their phylogenetic placement of ctenophores and the absence of several key bilaterian neuronal genes, it has been hypothesized that their neurons have evolved independently. Whether this is indeed the case remains unclear, and thus the evolutionary history of neurons is still contentious. Here, we have characterized the neuropeptide repertoire of the ctenophore Mnemiopsis leidyi. Using the machine learning NeuroPID tool1 129 new putative neuropeptide precursors were predicted. Sixteen of them are detected in the subepithelial nerve net (SNN), aboral organ (AO) and epithelial sensory cells (ESC) of early cydippid-stage M. leidyi by in situ hybridization (ISH) and immunohistochemistry (IHC). Four of these neuropeptides increase the animals swimming velocity in a behavioral essay. The new neuropeptides were used as markers to identify neuronal cell types in single cell transcriptomic data2. To unravel the neuronal architecture, we 3D reconstructed the SNN underlying the comb plates using serial block-face scanning electron microscopy (SBF-SEM). For the first time, we confirm a more than 100 years old hypothesis about anastomoses between neurites of the same cell in ctenophores and reveal that they occur through a continuous membrane. Our findings reveal the unique neuronal structure and neuropeptide repertoire of ctenophores and are important for reconstructing the evolutionary origin of animal neurons and nervous systems.

evolutionary biology↗