ОЦЕНКА СТРУКТУРНОЙ ГОМОЛОГИИ АБСЦИЗОВОЙ АЛЬДЕГИД-ОКСИДАЗЫ У ДРЕВЕСНЫХ РАСТЕНИЙ, ИСПОЛЬЗУЕМЫХ В АГРОЛЕСОМЕЛИОРАЦИИ НА ЮГЕ РОССИИ

Climate change leads to desertification and degradation of territories, which manifests itself in a decrease in the biodiversity of woody plants

There are various criteria for the selection of promising woody plants, one of which is the physiological and biochemical parameters of the species

Abscisic-aldehyde oxidase (AAO) is an enzyme that plays an important role in plant life processes under various adverse environmental conditions. This enzyme is involved in the formation and metabolism of abscisic acid (ABA). ABA is a plant hormone that affects processes such as seed and fruit maturation, seed germination, stomatal closure, and adaptation to stress conditions

The role of AAO is to catalyze the oxidation of abscisic aldehyde to ABA. AAO is activated in response to stress, leading to an increase in ABA levels in plants. A high ABA level acts as a signal of external stress and activates a cascade of reactions aimed at protecting the plant from adverse environmental conditions. During periods of water stress, ABA levels increase, causing stomata to close to reduce water loss. Features of ABA synthesis and metabolism are also determined by the environmental conditions. For example, the activity of enzymes involved in ABA formation and conversion increases during drought or other stress. Therefore, AAO plays an important role in plant protection and adaptation to stress conditions

The study of the role of AAO and ABA in plant metabolism is of great importance for understanding the mechanisms that ensure the survival and thriving of plants in arid conditions. Based on this, it is possible to select species for introduction into arid areas prone to desertification. 

Thus, the aim of this study was to identify differences in the structural homology of AAO in native and introduced woody plants used in agroforestry in the southern territories of Russia.

The AAO enzyme was chosen as a potential gene marker whose expression may reflect changes in the state of drought-stressed plants. Woody species were selected from the forest seed bank organization program for protective afforestation in the southern regions of Russia

1. Malus sylvestris: XP_050141529.1;

2. Populus alba A0A4V6A3J8;

3. Populus euphratica XP_011005929.1_1;

4. Populus trichocarpa: XP_024455533.2;

5. Prunus mume: XP_008230901.1;

6. Pyrus x bretschneideri: XP_048429325.1;

7. Quercus robur: XP_050284917.1.

Data on the structure of nucleotide and amino acid sequences of the studied genes of woody plants were obtained from the open-access databases UniProtKB

As a result of analyzing the similarity of the enzyme in woody plants, we found potential differences that may affect the plant's ability to adapt to drought (see Table 1, Fig. 1, 2, 3).

Populus trichocarpa is highly drought-resistant, while Malus sylvestris is poorly adapted to drought. The lowest percentage of similarity between the amino acid sequences of these trees is 69%. The similarity percentage between Populus trichocarpa and Prunus mume, Pyrus x bretschneideri, Quercus robur is approximately at the same level – 71%. The sequence of Malus sylvestris is most similar to Pyrus x bretschneideri. Prunus mume shows a high sequence similarity with both Malus sylvestris and Pyrus x bretschneideri. Since these trees are fruiting plants, their genetic sequences will be more similar to those of non-fruiting plants.

Figure 1 - Alignment of amino acid sequences of Malus sylvestris, Populus trichocarpa, Prunus mume, Pyrus x bretschneideri, and Quercus robur. Areas with a conservative level of more than 85% are colored dark gray

DOI:10.18454/jbg.2023.22.5.2

The amino acid sequence of Populus trichocarpa significantly differs in positions 4–19, 580–590, and 1352–1368. The presence of distinctive regions as the result of multiple alignment may indicate that these differences can play a role in functional variations between proteins. In this case, it is assumed that the difference in the sequence of the enzyme AAO may affect the process of ABA synthesis during drought. However, the enzyme has numerous conserved regions in its sequence among the considered tree species.

Figure 2 - Phylogram of the enzyme abscisic-aldehyde oxidase in woody plants

DOI:10.18454/jbg.2023.22.5.3

Phylogenetic analysis showed that Populus trichocarpa does not form clades with other tree species, highlighting its genetic difference from the other woody plant species. The clade with Malus sylvestris and Pinus x bretschneideri has 100% bootstrap support. The clade with Malus sylvestris, Pinus x bretschneideri, and Prunus mume has the same bootstrap support. These high values indicate a significant genetic similarity among these species. The absence of bootstrap support values for other nodes indicates that there is not enough data to calculate values. Closer to the common ancestor is Quercus robur, which means its sequence is more conservative among the plants. Pyrus x bretschneideri, Prunus mume, and Populus trichocarpa are further away from the common ancestor.

The evaluation of the structural homology of AAO in Malus sylvestris, Populus trichocarpa, Prunus mume, Pyrus x bretschneideri, and Quercus robur showed differences in several regions of the enzyme's amino acid sequence. This, in turn, may potentially influence the activity of the enzyme and the amount of its product involved in the formation of adaptive responses to drought

Figure 3 - Alignment of amino acid sequences of Populus alba, Populus euphratica, and Populus trichocarpa. Areas with a conservative level of more than 83% are colored dark gray

DOI:10.18454/jbg.2023.22.5.4

To find the same distinctive positions in the genus Populus, multiple alignment of the enzyme was carried out. The analysis revealed that the sequences between poplar trees are more than 95% similar. The whole sequence is conservative; there are only single substitutions in positions. The domain structures also overlap

[19]

. However, a region at the beginning of the sequences stands out: 1-23. Nevertheless, the genetic variability within the species can be further studied, as these variations may be associated with differences in ecological conditions or genetic diversity.

To find the same distinctive positions in the genus Populus, multiple alignment of the enzyme was carried out. The analysis revealed that the sequences between poplar trees are more than 95% similar. The whole sequence is conservative; there are only single substitutions in positions. The domain structures also overlap

Populus trichocarpa is one of the most drought-tolerant plants among the studied species of woody plants. The amino acid sequence of the enzyme AAO in Populus trichocarpa differs partially from other studied woody plants. The presence of these unique differences may influence the functional properties of the enzyme. In addition, phylogenetic analysis based on this enzyme shows that Populus trichocarpa is relatively isolated from other studied plants. It can be hypothesized that Populus trichocarpa has evolved and developed a unique amino acid sequence of the AAO enzyme. The amino acid sequence similarity between Populus alba, Populus euphratica, and Populus trichocarpa is over 95%. It is unknown whether these differences have functional significance in the enzyme. Presumably, these changes may be related to environmental differences or are a result of genetic diversity among poplar species.