In diploid organisms, phenotypic traits are often biased by effects known as Mendelian dominant-recessive interactions between inherited alleles. Phenotypic expression of SP11 alleles, which encodes the male determinants of self-incompatibility in Brassica rapa, is governed by a complex dominance hierarchy. Here, we show that a single polymorphic 24 nucleotide small RNA, named SP11 methylation inducer 2 (Smi2), controls the linear dominance hierarchy of the four SP11 alleles (S > S > S > S). In all dominant-recessive interactions, small RNA variants derived from the linked region of dominant SP11 alleles exhibited high sequence similarity to the promoter regions of recessive SP11 alleles and acted in trans to epigenetically silence their expression. Together with our previous study, we propose a new model: sequence similarity between polymorphic small RNAs and their target regulates mono-allelic gene expression, which explains the entire five-phased linear dominance hierarchy of the SP11 phenotypic expression in Brassica.
Thermoresponsive polymers having 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) moieties were fixed on the graphite surface by using the reversible addition-fragmentation chain transfer (RAFT) graft polymerization technique. The surface of graphite has been anodically oxidized by using our original electrochemical method, and then modified with 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoyloxy groups (RAFT reagents) by esterification with the corresponding acid chlorides. From the resulting RAFT reagent-modified graphite, 2,2,6,6-tetramethyl-4-piperidyl methacrylate (TEMPMA) and N-isopropylacrylamide (NIPAAm) monomers were copolymerized stepwise under RAFT polymerization conditions to afford the thermoresponsive block-copolymer-grafted graphite, poly(TEMPMA)-block-PNIPAAm-grafted graphite. N-Oxylation of tetramethylpiperidyl groups on the resulting graphite successfully afforded the corresponding TEMPO-containing thermoresponsive polymer-grafted graphite. Redox behavior of the resulting graphites was observed by cyclic voltammetry. The potential and intensity of the cathodic current peaks were discontinuously changed below and above the lower critical solution temperature (LCST) of the grafted thermoresponsive polymers. These results indicate that the phase transition of the thermoresponsive polymer on the graphite influences the electron transfer between the TEMPO moieties and the graphite surface.
Thermoresponsive and redox-active block copolymers having 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) moieties have been synthesized by using the reversible addition-fragmentation chain transfer (RAFT) polymerization technique.N-Isopropylacrylamide (NIPAAm) and 2,2,6,6-tetramethylpiperidyl methacrylate (TEMPMA) monomers were copolymerized stepwise under RAFT polymerization conditions to afford the thermoresponsive block copolymers, PNIPAAm-block-PTEMPMA and PNIPAAm-block-PTEMPMA-block-PNIPAAm. Oxidation of tetramethylpiperidine groups in the copolymers successfully afforded the corresponding TEMPO-containing block copolymers. The resulting triblock copolymer was found to be thermoresponsive showing lower critical solution temperature (LCST) at 34∘C in its aqueous solution. Redox behavior of the resulting copolymer was observed by cyclic voltammetry. The potential of anodic current peak changed below and above the LCST of the block copolymer. These results indicate that the phase transition of thermoresponsive polymer influences the redox potential of TEMPO moieties.
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