Insight into GABA shunt-associated aldehyde dehydrogenases (ALDH) and stress responses of ALDH superfamily in moss and barley

ABSTRACT We explored the expression of the aldehyde dehydrogenase (ALDH) superfamily in two model plants, Physcomitrium patens (moss) and Hordeum vulgare (barley), under various stress conditions. The ALDH enzymes are crucial for oxidizing aldehydes to carboxylic acids and are involved in multiple metabolic pathways. We found significant differences in enzyme expression between moss and barley within the same ALDH families. We then focused on the ALDH5, ALDH10, and ALDH21 families, which are part of the γ-aminobutyric acid (GABA) shunt, noting that the ALDH21 family is absent in barley. The kinetic properties of ALDH10 and ALDH5 enzymes were analyzed, revealing that PpALDH5F1 exhibits high specificity for succinic semialdehyde (SSAL), a product of GABA. The crystal structure of PpALDH5F1 identified key residues for SSAL binding. Knockout mutants of moss aldh5F2, aldh10A1, and aldh21A1 showed slightly smaller colonies than the wild-type. GABA and glutamate levels were elevated in aldh5F2 and aldh21A1 knockouts due to a partially blocked GABA shunt pathway, while aldh10A1 knockout showed no changes in GABA levels. Transcriptomic data revealed a link between several genes, including six upregulated glutathione-S-transferase genes in all three aldh knockouts, suggesting a direct compensatory mechanism for oxidative stress protection via conjugation of undegraded aldehydes to glutathione. Highlight Moss knockouts of GABA shunt-associated aldehyde dehydrogenases display slower growth, changes in levels of glutamate, glutamine and GABA, and result in upregulation of several unique glutathione-S-transferase genes. Competing Interest Statement The authors have declared no competing interest. Footnotes E-mail address for each author: David Jaroslav Kopečný: d.kopecny{at}upol.cz, Jakub Bělíček: jakub.belicek01{at}upol.cz, Martina Kopečná: martina.kopecna{at}upol.cz, Armelle Vigouroux: armelle.vigouroux{at}i2bc.paris-saclay.fr, Radka Končitíková: radka.koncitikova{at}gmail.com, Klaus von Schwartzenberg: klaus.von.schwartzenberg{at}uni-hamburg.de, Klára Končáková: klara.koncakova{at}upol.cz, Sanja Ćavar Zeljković: sanja.cavar{at}upol.cz, Miroslav Valárik: valarik{at}ueb.cas.cz, Karel Müller: muller{at}ueb.cas.cz, Roman Kouřil: roman.kouril{at}upol.cz, Veronique Bergougnoux: veronique.bergougnoux{at}upol.cz, Solange Moréra: solange.morera{at}i2bc.paris-saclay.fr David Kopečný: david.kopecny{at}upol.cz DATA AVAILABILITY The atomic coordinates and structure factors have been deposited in the Protein Data Bank (www.wwpdb.org) under accession codes 8OF3 for the apoform of PpALDH5F1, 8OFM for the PpALDH5F1 complex with NAD+ in an extended conformation and 8OF1 for the PpALDH5F1 complex with NAD+ in a contracted conformation. RNA-seq RAW datasets of moss aldh knockouts and WT were deposited in the NCBI Gene Expression Omnibus (GEO) database (https://www.ncbi.nlm.nih.gov/geo/) under accession code GSE299690. Differentially expressed genes from RNA-seq, qPCR data, metabolite, kinetic and ligand binding data were deposited in the Zenodo repository at https://doi.org/10.5281/zenodo.18186873. Other data are available in the Supplementary data.