Biology subjects

Pivato, M.

Publications and source records attributed to Pivato, M..

3 recordsLinked to original sources

bioRxiv2025

Heterologous expression of the cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase in Chlamydomonas reinhardtii causes increased cell size and biomass productivity in mixotrophic conditions

The Calvin-Benson-Bassham (CBB) cycle is the metabolic pathway responsible for CO assimilation in oxygenic photosynthetic organisms. Two key rate-limiting steps in this cycle are catalyzed by the enzymes fructose-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7-bisphosphatase (SBPase), making them promising targets for genetic enhancement to improve carbon fixation. A potential strategy involves overexpressing a cyanobacterial dual-function FBP/SBPase, which catalyzes both reactionsOverexpression of this enzyme in tobacco plants or in other plants led to an increase in growth rate and biomass accumulation. Here, the overexpression of the same enzyme was achieved in Chlamydomonas reinhardtii. The recombinant cyanobacterial FBP/SBPase isolated from C. reinhardtii exhibited the expected catalytic activity, being Mg2+ dependent and strongly activated in the presence of a reducing agent. The FBP/SBPase expressing lines exhibited an increased photosynthetic activity at the cell level and decreased production of singlet oxygen upon exposure to high irradiances, suggesting improved capacity to manage high excitation pressure of the photosynthetic apparatus. Increased cell volume was measured in FBP/SBPase-expressing lines under different growth conditions. However, increased growth and biomass productivity were observed only in mixotrophy when light and CO2 were limiting, leading to increased starch, protein, and lipid content on a cellular basis. This phenotype caused an increased sedimentation rate in the transformant lines: the expression of FBP/SBPase enzyme could thus be considered as a strategy to improve the cell harvesting process. These findings provide new insights into carbon metabolism in microalgae, and could, in the future, support improved biomass accumulation, paving the way for effective domestication and industrial use.

plant biology↗

bioRxiv2024

Abiotic stress-induced chloroplast and cytosolic Ca2+ dynamics in the green alga Chlamydomonas reinhardtii

Calcium (Ca2+)-dependent signalling plays a well-characterized role in the perception and response mechanisms to environmental stimuli in plant cells. In the context of a constantly changing environment, it is fundamental to understand how crop yield and microalgal biomass productivity are affected by external factors. Ca2+ signalling is known to be important in different physiological processes in microalgae but many of these signal transduction pathways still need to be characterized. Here, the role of compartment-specific Ca2+ signalling was investigated in Chlamydomonas reinhardtii in response to environmental stressors such as nutrient availability, osmotic stress, temperature fluctuations and carbon sensing. An in vivo single-cell imaging approach was adopted to directly visualize signalling processes at the level of specific subcellular compartments, using Chlamydomonas reinhardtii lines expressing a genetically encoded ratiometric Ca2+ indicator. Hyper-osmotic shock caused cytosolic and chloroplast Ca2+ elevations, whereas high temperature and inorganic carbon availability primarily induced Ca2+ transients in the chloroplast. In contrast, hypo-osmotic stress only induced Ca2+ elevations in the cytosol. The results herein reported show that compartment-specific signalling pathways are likely to play an important role in the response of Chlamydomonas to these stimuli providing new understanding of the mechanisms exploited by microalgae to respond to specific natural conditions.

plant biology↗

bioRxiv2022

Photosystem II monomeric antenna CP26 has a key role in Non-Photochemical Quenching in Chlamydomonas reinhardtii

O_LIThermal dissipation of the excitation energy harvested in excess, named non-photochemical quenching (NPQ), is one of the main photoprotective mechanisms evolved in oxygenic photosynthetic organisms. Here, the specific function in photoprotection and light harvesting of the monomeric Photosystem II antenna CP26, was investigated in Chlamydomonas, model organism for green algae C_LIO_LICRISPR/Cas9 genome editing and complementation strategies were applied to generate new cp26 knock-out mutants (named k6#) that differently from previous findings, did not negatively affected CP29 accumulation, allowing to compare mutants specifically deprived of CP26, CP29 or both C_LIO_LIThe absence of CP26 partially affected Photosystem II activity causing a reduced growth at low or medium light but not at high irradiances. However, the main phenotype observed in k6# mutants was a more than 70% reduction of NPQ compared to wild-type. This NPQ phenotype could be fully rescued by genetic complementation demonstrating that [~]50% of CP26 content compared to wild-type was sufficient to restore the NPQ capacity. C_LIO_LIOur findings demonstrate a pivotal role for CP26 in NPQ induction while CP29 has a crucial function for Photosystem II activity. The genetic engineering of these two proteins could be a promising strategy to regulate photosynthetic efficiency of microalgae under different light regimes. C_LI

plant biology↗