Abstract
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 (Solanum tuberosum) genome. For that, CK-related genes were retrieved from the sequenced genome of the S. tuberosum doubled monoploid (DM) Phureja group, classified and compared with Arabidopsis orthologs. Analysis of selected gene expression was performed with a transcriptome database for the S. tuberosum 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 RR genes, StRR1b, StRR11, and StRR18a are actively expressed, with StRR1b expressing most uniformly in all organs and StRR11 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→StHP1a→StRR1b/+; (2) shoot apical meristems, stolons, and mature tubers, StHK2/4→StHP1a→StRR1b/+; (3) stems and young tubers, StHK2/4→StHP1a→StRR1b/11/18a; and (4) roots and tuber sprouts, StHK4→StHP1a→StRR11/18a. CK synthesis genes StIPT3/5 and StCYP735A are expressed mainly in roots followed by tuber sprouts, but rather weakly in stolons and tubers. By contrast, CK-activation genes StLOGs are active in stolons, and StLOG3b expression is even stolon-confined. Apparently, the main CK effects on tuber initiation are realized via activity of StLOG1/3a/3b/7c/8a genes in stolons. Current advances and future directions in potato research are discussed.
Highlights
Potato tubers (Solanum tuberosum L.) are well known and widespread sources of food, feed, and technical substances
The background twocomponent system (TCS) activity of these proteins seems to be sufficient to rescue the basic phenotype of Arabidopsis triple mutants lacking all three CK receptors and no longer responding to CKs (Higuchi et al, 2004; Nishimura et al, 2004; Riefler et al, 2006; Romanov, 2009)
We present a global view on the CK regulatory system in potatoes
Summary
Potato tubers (Solanum tuberosum L.) are well known and widespread sources of food, feed, and technical substances (starches). The background TCS activity of these proteins seems to be sufficient to rescue the basic phenotype of Arabidopsis triple mutants lacking all three CK receptors and no longer responding to CKs (Higuchi et al, 2004; Nishimura et al, 2004; Riefler et al, 2006; Romanov, 2009) All this indicates the possible role of CKI1 and ETR1 in MSP signaling. By means of cluster analysis of the organ-specific expression of genes encoding receptors and StRRs type B (Supplementary Figure 5), we identified four types of prevailing signaling chains: (1) in leaves and flowers, StHK2/3→StHP1a→StRR1b/+; (2) in shoot apical meristems, stolons, and mature tubers, StHK2/4→StHP1a→StRR1b/+; (3) in stems and young tubers, StHK2/4→StHP1a→StRR1b/11/18a; and (4) in roots and tuber sprouts, StHK4→StHP1a→StRR11/18a. The expression patterns of remaining CK-related genes coincide moderately
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