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Trihelix transcription factors are involved in the growth and development of plants, as well as various stress responses. In this work, we have identified 37 genes of the trihelix family in the apple genome (MdTH). They were located on 13 chromosomes. Phylogenetic analysis showed that apple trihelix transcription factors belong to one of six subfamilies (GT-1, GT-2, SH4, SIP1, GTγ and GTδ). Genes from different groups have differences in the gene structure and conserved functional domains. Analysis of the promoter regions of apple trihelix transcription factors showed that their expression may be regulated by light, phytohormones, stress factors such as anaerobic stress, drought, low temperature, a pathogen attack, an injury, etc. In our work, we have demonstrated that drought, salinity, as well as high and low temperatures, affect the expression of genes of the apple trihelix family. Among the genes under study, the greatest increase in the expression level under soil salinity was observed in MdTH4 and MdTH24 genes. The MdTH4 gene also showed the greatest increase in the relative expression level during drought. With decreasing temperature, the greatest change in the expression level was observed in MdTH30. The same gene was among the three genes whose expression level was significantly decreasing when exposed to drought. With an increase in temperature, the expression level of three genes demonstrated the greatest increase: MdTH8, MdTH20, and MdTH36.

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Stress-associated proteins (SAPs) are the transcription factors containing the zinc-finger domains A20 and/or AN1. Genome-wide identification and characterization of an apple variety of Golden Delicious stress-associated proteins was performed, potential SAPs were found. Each of them contains, at least, one zinc-finger domain AN1. A phylogenetic tree was constructed on the basis of the amino acid sequences of apple SAP and homologues from other species (dicotyledonous cotton and monocotyledonous rice) to assess their phylogenetic relationships. The sequences ahead of the translation initiation site of SAPs genes were analyzed to discover cis-elements involved in the gene expression regulation. The analysis shows that apple SAPs are involved in a complex network of regulatory elements that controls the vitality of plant cells. It can be assumed that the expression of SAPs in apple trees occurs constantly, but if conditions of a plant growth are changed, their level increases. Regulation of the SAP expression may depend on a plant ontogenesis stage and it may vary in different tissues.

Aim. The aim of this work was to study the variability of the gene MDP0000151428, which belongs to the DREB family, among varieties of different genetic origin, which have different resistance to cold. Methods. Polymorphism was analyzed by PCR and sequencing. Results. Cloning and sequencing of the gene MDP0000151428 from 18 varieties and species of apple with different levels of resistance to cold have been carried out. An assessment of the variability of its primary structure showed the presence of point mutations. Most of them were single nucleotide substitutions, in one case a single nucleotide deletion was observed. The degree of sequence identity ranged from 97.5 % to 100 %. Conclusions. Evaluation of polymorphism of gene length MDP0000151428 showed that it is quite conservative and does not carry extended insertions or deletions in 20 varieties and species of apple trees with different levels of resistance to cold. The analysis showed that the frequency of occurrence of mutations in different sites of the gene MDP0000151428 differs. The nucleotides in 138, 341 and 472 positions are most susceptible to mutations. Comparison of hypothetical amino acid sequences showed the presence of separate substitutions. Most often they occur in 114 and 158 positions. Keywords: apple tree, gene MDP0000151428, transcription factors, resistance to cold.