Membrane receptors of cytokinin and their regulatory role in Arabidopsis thaliana plant response to photooxidative stress under conditions of water deficit

Mild photooxidative stress combined with water deficit affected the expression of genes of cytokinin (CK) signal transduction. According to qRT-PCR data, these stress factors suppressed the expression of CK receptor genes AHK2 and AHK3 and the ARR5 response regulator gene, and slightly activated the expression of AHK4 gene. The absence of AHK2 and AHK3 receptors in Arabidopsis thaliana (L.) Heynh. mutants affected markedly the content of low-molecular-weight antioxidants (anthocyanins, carotenoids, proline) and resulted in the CK-dependent changes in the expression of genes, markers of oxidative stress, including RAB18, CHS, P5CS1, and PRODH1, under both normal and stressful conditions. At the same time, knockout of a single receptor gene or their combination did not induce CK-specific changes in the stress-activated expression of AOX1a, the marker gene of oxidative stress. CK receptor mutants lacked a statistically significant genotype influence on the photosystem II and photosystem I fluorescence yield under normal and stressful conditions. However, the system of CK perception was shown to be involved in the transcription regulation of the genes of the photosynthetic apparatus, ELIP2 and PSBS. Thus, CKs play an important role in plant responses to the photooxidative stress. The inactivation of the CK signaling system components proves to be one of the main strategies of Arabidopsis plant adaptation to the high light under conditions of water deficit.