Biology subjects

Barbieri, G.

Publications and source records attributed to Barbieri, G..

3 recordsLinked to original sources

bioRxiv2025

Wave-like SnRK1 Activation and Tre6P-Sucrose Imbalance Shape Early Salt Stress Response in Growing Alfalfa Leaves

Alfalfa (Medicago sativa L.) is a key forage crop valued for its adaptability and nutritional quality, yet salinity significantly limits its productivity, particularly in arid regions. Understanding early stress responses is crucial for improving resilience. Salt stress impairs leaf growth and photosynthesis, triggering complex, time-dependent signaling. Sucrose non-fermenting kinase 1 (SnRK1), a central metabolic sensor, regulates metabolism and growth under stress. We investigated the dynamics of SnRK1, sucrose, and trehalose-6- phosphate (Tre6P) during leaf expansion in a salt-tolerant alfalfa cultivar. Plants were hydroponically grown and exposed to 200 mM NaCl. Stress induced transient declines in chloroplast performance (Fv/Fm, performance index). SnRK1 activity peaked within 1 hour post-treatment (hpt), likely initiating metabolic shifts. By 3 hpt, sugar metabolism shifted, with increased catabolism, TCA cycle modulation, and glucose-6-phosphate accumulation. SnRK1 and sucrose showed opposing wave-like patterns, with sucrose peaking at 1 day post-treatment (dpt) as Tre6P declined, indicating a disrupted regulatory link. A second SnRK1 peak at 3 dpt correlated with reduced leaf growth. Exogenous sucrose inhibited SnRK1, while NaCl enhanced it. This is the first report of wave-like SnRK1 activation and Tre6P-sucrose uncoupling in alfalfa, highlighting early SnRK1 activation as key to salt stress adaptation. HighlightsO_LIEarly SnRK1 activation is a key determinant of salt stress response in alfalfa, linking early biochemical shifts to downstream metabolic alteration. C_LIO_LIFirst evidence of a wave-like SnRK1 activation pattern and disruption of the Tre6P- Sucrose nexus reveals novel dynamics in alfalfas stress signaling. C_LIO_LISucrose inhibits SnRK1 activity in source leaves with or without NaCl C_LI

plant biology↗

bioRxiv2024

The conserved membrane-proximal domain of Sbh1/ Sec61β guides signal peptides into the Sec61 channel

In eukaryotes, protein secretion begins with protein translocation through the universally conserved Sec61 channel into the endoplasmic reticulum (ER). Its {beta}-subunit, Sbh1 in yeast, enhances ER import of proteins with specific suboptimal signal peptides by an unknown mechanism. The Sbh1 cytosolic N-terminus consists of an intrinsically disordered, non-conserved region (IDR) that has never been visualized in active channel structures, but is close to the translocating polypeptide in the cytosolic channel vestibule. The Sbh1/Sec61{beta} N-terminal IDR is followed by structured 15 amino acids and its C-terminal transmembrane helix, both of which are conserved. We show here that the proline and adjacent conserved residues at the Sbh1 cytosolic/transmembrane domain interface form a hinge that positions the Sbh1 cytosolic domain across the channel vestibule and orients it with respect to the lateral gate. This orientation is critical for Sbh1-dependent protein insertion into the channel. Sbh1-dependence of Sec61 channel insertion is a function of the signal peptide of the respective secretory protein. By chemical crosslinking of purified cytosolic domains of Sbh1 and its paralog Sbh2 to synthetic signal peptides derived from their respective client proteins, we show that the cytosolic domains of Sbh1 and Sbh2 contain specific signal peptide binding sites. The position of the crosslinked residues suggests that signal peptide binding is mediated by the IDRs. We conclude that Sec61{beta} homologs directly recognize signal peptides of their substrates and guide them into the Sec61 channel; they thus control entry of specific proteins into the secretory pathway.

biochemistry↗

bioRxiv2022

ER translocation of suboptimal targeting sequences depends on Sec61β/Sbh1 and its phosphorylation

The endoplasmic reticulum (ER) protein translocation channel subunit Sec61{beta}/Sbh1 is non-essential, but contains multiple phosphorylation sites suggesting a regulatory role in ER protein import. We show here that mutating two N-terminal, proline-flanked, phosphorylation sites in the Sbh1 cytosolic domain phenocopies the temperature-sensitivity of a yeast strain lacking SBH1/SBH2, and results in reduced translocation into the ER of an Sbh1-dependent substrate, Gls1. In a microscopic screen we show that about 12% of GFP-tagged secretory proteins depend on Sbh1 for translocation. Sbh1-dependent proteins have targeting sequences with less pronounced hydrophobicity and often no or an inverse charge bias. A subset of these proteins was dependent on N-terminal phosphorylation of Sbh1 and on the phospho-S/T-specific proline isomerase Ess1 (PIN1 in mammals) for ER import. We conclude that Sbh1 promotes ER translocation of substrates with suboptimal targeting sequences and that its activity is regulated by a conformational change induced by N-terminal phosphorylation.

biochemistry↗