Global View on the Cytokinin Regulatory System in Potato.

Cytokinins (CKs) were earlier shown to promote potato tuberization. Our study aimed to identify and characterize CK-related genes which constitute CK regulatory system in the core potato () genome. For that, CK-related genes were retrieved from the sequenced genome of the doubled monoploid (DM) Phureja group, classified and compared with Arabidopsis orthologs. Analysis of selected gene expression was performed with a transcriptome database for the heterozygous diploid line RH89-039-16. Genes responsible for CK signaling, biosynthesis, transport, and metabolism were categorized in an organ-specific fashion. According to this database, CK receptors StHK2/3 predominate in leaves and flowers, StHK4 in roots. Among phosphotransmitters, StHP1a expression largely predominates. Surprisingly, two pseudo-phosphotransmitters intended to suppress CK effects are hardly expressed in studied organs. Among B-type genes, , , and are actively expressed, with expressing most uniformly in all organs and exhibiting the highest expression in roots. By cluster analysis four types of prevailing CK-signaling chains were identified in (1) leaves and flowers, StHK2/3→ 1→StRR1b/+; (2) shoot apical meristems, stolons, and mature tubers, StHK2/4→ 1→StRR1b/+; (3) stems and young tubers, StHK2/4→ 1→StRR1b/11/18a; and (4) roots and tuber sprouts, StHK4→ 1→StRR11/18a. CK synthesis genes / and are expressed mainly in roots followed by tuber sprouts, but rather weakly in stolons and tubers. By contrast, CK-activation genes are active in stolons, and expression is even stolon-confined. Apparently, the main CK effects on tuber initiation are realized via activity of genes in stolons. Current advances and future directions in potato research are discussed.