GENE EXPRESSION OF TEA MICROPLANTS (CAMELLIA SINENSIS (L.) KUNTZE) CAUSED BY THE ACTION OF OSMOTIC STRESS IN VITRO

Osmotic stress caused by drought is the main abiotic environmental factor that reduces the growth and yield of tea plants. Therefore, the main research on tea breeding is aimed at creating new cultivars resistant to water deficiency. Modern biotechnological techniques can increase the effectiveness of traditional methods in creating new genotypes as donors of resistance to this stress factor. When obtaining forms resistant to drought, a certain selective factor is introduced into the nutrient medium to simulate the effect of stress in vitro. In the present study, osmotic stress was caused by the addition of mannitol to the nutrient medium to identify genetic reactions in tea microshoots in vitro. It was found that the expression level of genes such as DHN2, LOX1, LOX6, BAM, SUS1, TPS11, RS1, RS2 and SnRK1.3 was increased 2–10 times during osmotic stress caused by mannitol, while the expression of many other stress-related genes did not significantly change. At the same time, suppression of the following genes was observed: bHLH12, bHLH7, bHLH21, bHLH43, CBF1, WRKY2, SWEET1, SWEET2, SWEET3, INV5 and LOX7. During this study, two main groups of genes with a high degree of correlation were found. The first group included seven genes, namely: CBF1, DHN3, HXK2, SnRK1.1, SPS, SWEET3 and SWEET1. The second group consisted of eight genes, including: DHN2, SnRK1.3, HXK3, RS1, RS2, LOX6, SUS4 and BAM5. A high level of correlation indicates a high bond strength of genes that can be co-expressed or can be associated with regulons. The present study demonstrates that micro-shoots of tea undergo a number of adaptations to cope with osmotic stress in vitro. However, some important genes that are associated with stress were turned off or suppressed osmoregulation in microshoots. Of the 31 genes studied, 9 genes (DHN2, BAM, SUS4, RS1, RS2, SnRK1.3, TPS11, LOX1 and LOX6) were significantly activated in tea microshoots leaves under the action of mannitol, six of them are associated with sugar metabolism. These genes can be proposed as reliable markers of the tea plant's response to drought.