Aldehyde dehydrogenases (ALDHs) represent a superfamily of NAD(P)+-dependent enzymes that catalyze oxidation of aldehydes to carboxylic acids. Aldehydes are known for being highly reactive and toxic at higher concentrations and ALDHs play a crucial role in detoxifying aldehydes produced by various metabolic pathways and during various stress conditions such as salinity, heat, cold and drought. At least 13 ALDH distinct families are found in plants. ALDHs sharing more than 40% sequence identity belong to the same family. ALDHs share a common fold of three domains and carry a catalytic cysteine residue. While certain algae genomes contain up to nine ALDH genes, the genome of a moss Physcomitrella patens already comprises 21 genes sorted in many more families. Therefore, the moss Physcomitrella represents an important non-vascular plant model to study an evolution of ALDH genes.
Here, we focused on ALDH2, ALDH10 and ALDH12 family members from the moss and compare them with their orthologues in maize (Zea mays). Plant ALDH2 family comprises mitochondrial and cytosolic isoforms split into ALDH2B and ALDH2C subfamilies, respectively. While mitochondrial ALDH2 isoforms display acetaldehyde activity across the whole plant kingdom, the role of cytosolic isoforms is much more diverse. They can oxidize various aliphatic and aromatic aldehydes including benzaldehyde or coniferaldehyde from phenylpropanoid pathway and many others. The genome of P. patens contains two ALDH2 genes coding for PpALDH2A (belonging to ALDH2C subfamily) and PpALDH2B from ALDH2B subfamily. ALDH10 family represents peroxisomal aminoaldehyde dehydrogenases also known as betaine aldehyde dehydrogenases and the family is represented only by a single ALDH10 gene in moss. Finally, the ALDH12 family represents mitochondrial Δ1-pyrroline-5-carboxylate dehydrogenases (P5CDHs). There is usually a single ALDH12 gene in both lower and higher plants. P5C is an oxidation product of proline. Proline is known to accumulate in plants during various environmental stresses including drought, high salinity, high light and other oxidative and biotic stresses. We performed X-ray crystallographic study combined with site-directed mutagenesis and enzyme kinetics to analyze active sites and to identify key residues affecting the substrate or coenzyme preferences of above mentioned ALDH family members.
This work was supported by the grant 18-07563S from the Czech Science Foundation, the MOBILITY grant 7AMB17DE009 and the grant LO1204 from the National Program of Sustainability I by the Ministry of Education, Youth and Sports, Czech Republic and internal grants IGA_PrF_2017_016 and IGA_PrF_2018_033 from Palacký University Olomouc.