Biology subjects

Tagliani, A.

Publications and source records attributed to Tagliani, A..

3 recordsLinked to original sources

bioRxiv2024

A missense mutation in the gene encoding the Mg-chelatase subunit I leads to a viable pale green line with phenotypic features of potential interest for barley breeding programs

The pale green trait, i.e. reduced chlorophyll content, has been shown to increase the efficiency of photosynthesis and biomass accumulation when photosynthetic microorganisms and tobacco plants are cultivated at high densities. Thus, the hus1 barley mutant is defective in photosystem antenna biogenesis, and exhibits a 50% reduction in leaf chlorophyll content. Nevertheless, its agronomical performance under standard field conditions is comparable to that of the wild-type. This supports the notion that crops can decrease their investment in antenna proteins and chlorophyll biosynthesis without detrimental effects on productivity. Here, we assess the effects of reducing leaf chlorophyll content in barley by altering the chlorophyll biosynthesis pathway (CBP). To this end, we have isolated and characterised the pale green barley mutant xan-h.chli-1, which carries a missense mutation in the Xan-h gene for subunit I of Mg-chelatase (HvCHLI), the first enzyme in the CBP. Intriguingly, xan-h.chli-1 is the only known viable homozygous mutant at the Xan-h locus in barley. The Arg298Lys amino-acid substitution in the ATP-binding cleft causes a slight decrease in HvCHLI protein abundance, and a marked reduction in Mg-chelatase activity. Under controlled growth conditions, mutant plants display reduced accumulation of antenna and photosystem core subunits, together with reduced photosystem II yield relative to wild type under moderate illumination, and consistently higher than wild-type levels at high light intensities. Moreover, the reduced content of leaf chlorophyll is associated with a stable reduction in daily transpiration rate, and slight decreases in total biomass accumulation and water-use efficiency. These traits are reminiscent of phenotypic features of wild barley accessions and landraces that thrive under arid climatic conditions. Overall, our findings make the xan-h.chli-1 allelic variant of potential interest for tailoring barley, and other crop plants, for growth in harsh environments.

plant biology↗

bioRxiv2022

Structural snapshots of nitrosoglutathione binding and reactivity underlying S-nitrosylation of photosynthetic GAPDH

S-nitrosylation is a redox post-translational modification widely recognized to play an important role in cellular signaling as it can modulate protein function and conformation. At the physiological level, nitrosoglutathione (GSNO) is considered the major physiological NO-releasing compound due to its ability to transfer the NO moiety to protein thiols. GSNO can also induce protein S-glutathionylation but the structural determinants regulating its redox specificity are not fully elucidated. In this study, we employed photosynthetic glyceraldehyde-3-phosphate dehydrogenase from Chlamydomonas reinhardtii (CrGAPA) to investigate the molecular mechanisms underlying GSNO-dependent thiol oxidation. We first observed that GSNO causes enzyme inhibition by specifically inducing S-nitrosylation. Treatment with reducing agents restores CrGAPA activity completely. While the cofactor NADP+ only partially protects from GSNO-mediated S-nitrosylation, the resultant inactivation is completely blocked by the presence of the substrate 1,3-bisphosphoglycerate, indicating that the S-nitrosylation of the catalytic Cys149 is responsible of CrGAPA inactivation. The crystal structures of CrGAPA in complex with NADP+ and NAD+ reveal a general structural similarity with other photosynthetic GAPDH. Starting from the 3D structure, we carried out molecular dynamics simulations to identify the protein residues involved in GSNO binding. Quantum mechanical/molecular mechanical calculations were performed to investigate the reaction mechanism of GSNO with CrGAPA Cys149 and to disclose the relative contribution of protein residues in modulating the activation barrier of the trans-nitrosylation reaction. Based on our findings, we provide functional and structural insights into the response of CrGAPA to GSNO-dependent regulation, possibly expanding the mechanistic features to other protein cysteines susceptible to be oxidatively modified by GSNO.

plant biology↗

bioRxiv2020

Structural and functional insights into nitrosoglutathione reductase from Chlamydomonas reinhardtii

Protein S-nitrosylation plays a fundamental role in cell signaling and nitrosoglutathione (GSNO) is considered as the main nitrosylating signaling molecule. Enzymatic systems controlling GSNO homeostasis are thus crucial to indirectly control the formation of protein S-nitrosothiols. GSNO reductase (GSNOR) is the key enzyme controlling GSNO levels by catalyzing its degradation in the presence of NADH. Here, we found that protein extracts from the microalga Chlamydomonas reinhardtii catabolize GSNO via two enzymatic systems having specific reliance on NADPH or NADH and different biochemical features. Scoring the Chlamydomonas genome for orthologs of known plant GSNORs, we found two genes encoding for putative and almost identical GSNOR isoenzymes. One of the two, here named CrGSNOR1, was heterologously expressed and purified. The kinetic properties of CrGSNOR1 were determined and the high-resolution three-dimensional structures of the apo and NAD+-bound forms of the enzyme were solved. These analyses revealed that CrGSNOR1 has a strict specificity towards GSNO and NADH, and a conserved 3D-folding with respect to other plant GSNORs. The catalytic zinc ion, however, showed an unexpected variability of the coordination environment. Furthermore, we evaluated the catalytic response of CrGSNOR1 to thermal denaturation, thiol-modifying agents and oxidative modifications as well as the reactivity and position of accessible cysteines. Despite being a cysteine-rich protein, CrGSNOR1 contains only two solvent-exposed/reactive cysteines. Oxidizing and nitrosylating treatments have null or limited effects on CrGSNOR1 activity, highlighting a certain resistance of the algal enzyme to redox modifications. The molecular mechanisms and structural features underlying the response to thiol-based modifications are discussed. One-sentence summaryGSNOR1 from Chlamydomonas reinhardtii displays an unusual variability of the catalytic zinc coordination environment and an unexpected resistance to thiol-based redox modifications

plant biology↗