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Cold stress imposes a great physiological impact on most photosynthetic organisms. The acclimation to cold is very poorly studied in microalgae, even though understanding the molecular mechanisms underlying their cold tolerance has implications for biotechnological applications, such as the development of cold‐tolerant strains for industrial purposes. Scenedesmus sp. B2‐2 is a Nordic strain of green freshwater microalgae that thrives in cold conditions. Here, we analyzed transcriptomic changes of B2‐2 when exposed to the cold (5°C) and compared it to a control grown at 25°C. The aim was to understand more about the mechanisms underlying B2‐2's adaptation to low temperatures. We studied differentially expressed genes (DEGs) related to lipid synthesis, carbon metabolism and photosynthesis. Scenedesmus sp. B2‐2 produced more lipids when exposed to cold conditions and did not reduce its carbon metabolism or photosynthetic processes. 24 putative cold‐responsive genes were found to be non‐responsive in Scenedesmus sp. B2‐2 when grown at 5°C. These genes could serve as targets for genetic engineering to enhance cold tolerance in algal strains used in biotechnology. We also studied B2‐2´s cell wall changes in response to cold by measuring cell wall thickness at 1, 4, 12, 24, 48, 72, 120 and 240 hours of cold exposure and correlating the results to the transcriptomic data. The results show that the cell wall thickens with increased duration of cold exposure. Several glycosyltransferases were found to be significantly up‐regulated throughout cold exposure and may play a role in cell wall thickening. [ABSTRACT FROM AUTHOR]

Metacaspases are cysteine proteases present in plants, fungi and protists. While the association of metacaspases with cell death is studied in a range of organisms, their native substrates are largely unknown. Here, we explored the in vivo proteolytic landscape of the two metacaspases, CrMCA‐I and CrMCA‐II, present in the green freshwater alga Chlamydomonas reinhardtii, using mass spectrometry‐based degradomics approach, during control conditions and salt stress. Comparison between the cleavage events of CrMCA‐I and CrMCA‐II in metacaspase mutants revealed unique cleavage preferences and substrate specificity. Degradome analysis demonstrated the relevance of the predicted metacaspase substrates to the physiology of C. reinhardtii cells and its adaptation during salt stress. Functional enrichment analysis indicated an involvement of CrMCA‐I in the catabolism of carboxylic acids, while CrMCA‐II plays an important role in photosynthesis and translation. Altogether, our findings suggest distinct cellular functions of the two metacaspases in C. reinhardtii during salt stress response. [ABSTRACT FROM AUTHOR]

With climate change, droughts are expected to be more frequent and severe, severely impacting plant biomass and quality. Here, we show that overexpressing the Arabidopsis gene AtFtsHi3 (FtsHi3OE) enhances drought‐tolerant phenotypes without compromising plant growth. AtFtsHi3 encodes a chloroplast envelope pseudo‐protease; knock‐down mutants (ftshi3‐1) are found to be drought tolerant but exhibit stunted growth. Altered AtFtsHi3 expression therefore leads to drought tolerance, while only diminished expression of this gene leads to growth retardation. To understand the underlying mechanisms of the enhanced drought tolerance, we compared the proteomes of ftshi3‐1 and pFtsHi3‐FtsHi3OE (pFtsHi3‐OE) to wild‐type plants under well‐watered and drought conditions. Drought‐related processes like osmotic stress, water transport, and abscisic acid response were enriched in pFtsHi3‐OE and ftshi3‐1 mutants following their enhanced drought response compared to wild‐type. The knock‐down mutant ftshi3‐1 showed an increased abundance of HSP90, HSP93, and TIC110 proteins, hinting at a potential downstream role of AtFtsHi3 in chloroplast pre‐protein import. Mathematical modeling was performed to understand how variation in the transcript abundance of AtFtsHi3 can, on the one hand, lead to drought tolerance in both overexpression and knock‐down lines, yet, on the other hand, affect plant growth so differently. The results led us to hypothesize that AtFtsHi3 may form complexes with at least two other protease subunits, either as homo‐ or heteromeric structures. Enriched amounts of AtFtsH7/9, AtFtsH11, AtFtsH12, and AtFtsHi4 in ftshi3‐1 suggest a possible compensation mechanism for these proteases in the hexamer. [ABSTRACT FROM AUTHOR]

This article discusses the potential of photosynthetic organisms, such as algae and cyanobacteria, to address challenges related to climate change, energy use, and food security. These organisms use solar energy to convert carbon dioxide into organic molecules, which can be used for fuel, chemical production, food, and feed. However, there are still scientific and economic challenges to overcome in order to make this concept economically feasible. The article also highlights current research and developments in the field, including studies on plant growth, chlorophyll fluorescence, and the biotechnological exploitation of microalgae. [Extracted from the article]