The Crosstalk between Cytokinin and Auxin Signaling Pathways in the Control of Natural Senescence ofArabidopsis thalianaLeaves

Natural senescence of leaves is a regular physiological process subjected to a certain genetic program and controlled by various phytohormones. Cytokinins (CKs) play a crucial role in the leaf-senescence control being negative regulators of this process. We previously reported on the prolonged vegetative growth and the development of a double knockoutahk2ahk3mutant ofArabidopsis thalianaHeynh. (L.) for the genes encoding CK receptors. According to the data of the transcriptomic analysis and real-time RT-PCR of selected genes performed in this study, the delay of leaf senescence inahk2ahk3mutants is accompanied by enhanced (4-281-fold) expression of the group ofSAUR(small auxin-up RNA) genes encoding auxin response proteins and by upregulation of theSSPP(senescence-suppressed protein phosphatase) gene, whose expression level significantly (137-fold) exceeded that in a wild-type transcriptome. Thus, it is quite possible that under significant inhibition of the CK signaling leaf senescence inArabidopsisplants regulated via a compensatory mechanism connected with changes in the expression of theSAURgene family and a certain pool of genes related to the auxin transport and signaling.