Large-scale high-throughput plant phenotyping (sometimes called phenomics) is becoming increasingly important in plant biology and agriculture and is essential to cutting-edge plant breeding and management approaches needed to meet the food and fuel needs for the next century. Currently, the application of these approaches is severely limited by the availability of appropriate instrumentation and by the ability to communicate experimental protocols, results and analyses. To address these issues, we have developed a low-cost, yet sophisticated open-source scientific instrument designed to enable communities of researchers, plant breeders, educators, farmers and citizen scientists to collect high-quality field data on a large scale. The MultispeQ provides measurements in the field or laboratory of both, environmental conditions (light intensity and quality, temperature, humidity, CO2 levels, time and location) and useful plant phenotypes, including photosynthetic parameters—photosystem II quantum yield (ΦII), non-photochemical exciton quenching (NPQ), photosystem II photoinhibition, light-driven proton translocation and thylakoid proton motive force, regulation of the chloroplast ATP synthase and potentially many others—and leaf chlorophyll and other pigments. Plant phenotype data are transmitted from the MultispeQ to mobile devices, laptops or desktop computers together with key metadata that gets saved to the PhotosynQ platform (https://photosynq.org) and provides a suite of web-based tools for sharing, visualization, filtering, dissemination and analyses. We present validation experiments, comparing MultispeQ results with established platforms, and show that it can be usefully deployed in both laboratory and field settings. We present evidence that MultispeQ can be used by communities of researchers to rapidly measure, store and analyse multiple environmental and plant properties, allowing for deeper understanding of the complex interactions between plants and their environment.

Summary• Guard cell movements are regulated by environmental cues including, for example, elevations in extracellular Ca 2+ concentration. Here, the subcellular localization and physiological function of the Ca 2+ -sensing receptor (CAS) protein was investigated.• CAS protein localization was ascertained by microscopic analyses of green fluorescent protein (GFP) fusion proteins and biochemical fractionation assays. Comparative guard cell movement investigations were performed in wild-type and cas lossof-function mutant lines of Arabidopsis thaliana. Cytoplasmic Ca 2+ dynamics were addressed in plants expressing the yellow cameleon reporter protein YC3.6.• This study identified CAS as a chloroplast-localized protein that is crucial for proper stomatal regulation in response to elevations of external Ca 2+. CAS fulfils this role through modulation of the cytoplasmic Ca 2+ concentration.• This work reveals a novel role of the chloroplast in cellular Ca 2+ signal transduction.

Under anaerobic conditions, several species of green algae perform a light-dependent hydrogen production catalyzed by a special group of [FeFe] hydrogenases termed HydA. Although highly interesting for biotechnological applications, the direct connection between photosynthetic electron transport and hydrogenase activity is still a matter of speculation. By establishing an in vitro reconstitution system, we demonstrate that the photosynthetic ferredoxin (PetF) is essential for efficient electron transfer between photosystem I and HydA1. To investigate the electrostatic interaction process and electron transfer between PetF and HydA1, we performed site-directed mutagenesis. Kinetic analyses with several site-directed mutagenesis variants of HydA1 and PetF enabled us to localize the respective contact sites. These experiments in combination with in silico docking analyses indicate that electrostatic interactions between the conserved HydA1 residue Lys 396 and the C terminus of PetF as well as between the PetF residue Glu 122 and the N-terminal amino group of HydA1 play a major role in complex formation and electron transfer. Mapping of relevant HydA1 and PetF residues constitutes an important basis for manipulating the physiological photosynthetic electron flow in favor of light-driven H 2 production.Among all photosynthetic organisms, only green algae can couple light-driven electron transport originating from water splitting with hydrogen production (1). Hydrogen evolution in the unicellular green alga Chlamydomonas reinhardtii is naturally induced upon nutrient deprivation (2). Especially in the absence of sulfur, the photosynthetic oxygen evolution rate drops below the respiratory rate leading to intracellular anaerobiosis. Under anaerobic conditions, the oxygen-sensitive (2, 3) [FeFe] hydrogenase HydA is synthesized and catalyzes light-dependent H 2 production, thereby dissipating excess redox equivalents under conditions in which the Calvin cycle is down-regulated (4).The extraordinarily small monomeric [FeFe] hydrogenases of green algae only consist of the catalytic core unit containing the active site (H-cluster), whereas other [FeFe] hydrogenases possess an additional N-terminal F-domain harboring one to four accessory iron-sulfur clusters (5, 6). Because Chlorophytatype [FeFe] hydrogenases lack any accessory clusters (7, 8), a direct electron transfer between the native electron donor and the H-cluster has been assumed (9, 10). In C. reinhardtii, HydA1 has been shown to be localized in the chloroplast stroma (11), and first kinetic examinations with purified proteins demonstrated that the plastidic ferredoxin PetF can interact with HydA1. These results and the fact that H 2 production in C. reinhardtii is photosystem I (PSI) 2 -dependent (4) led to the hypothesis that PetF is the native electron donor of the plastidic hydrogenase (12). Derived from in silico analyses, two possible PetF-HydA2 electron transfer complex models were recently suggested (13). However, in contrast to the well studied interacti...

Supplementary data are available at Bioinformatics online.

Photosystem I is defined as plastocyanin-ferredoxin oxidoreductase. Taking advantage of genetic engineering, kinetic analyses and cryo-EM, our data provide novel mechanistic insights into binding and electron transfer between PSI and Pc. Structural data at 2.74 Å resolution reveals strong hydrophobic interactions in the plant PSI-Pc ternary complex, leading to exclusion of water molecules from PsaA-PsaB / Pc interface once the PSI-Pc complex forms. Upon oxidation of Pc, a slight tilt of bound oxidized Pc allows water molecules to accommodate the space between Pc and PSI to drive Pc dissociation. Such a scenario is consistent with the six times larger dissociation constant of oxidized as compared to reduced Pc and mechanistically explains how this molecular machine optimized electron transfer for fast turnover.