From tRNA modification to cytokinins - Characterisation of tRNA-mediated cytokinin biosynthesis in the early land plant Physcomitrella

我们收集到的证据表明，与种子植物不同，苔藓小立壶菌的植物激素细胞分裂素（腺嘌呤的异戊基衍生物）完全来自tRNA。因此，我们假设在陆地植物进化的早期阶段，tRNA-异戊烯基转移酶（tRNA- ipts）催化的tRNA异戊烯化承担了为作为植物激素的游离细胞分裂素提供前体的功能。这种tRNA-IPT介导的细胞分裂素生物合成途径在种子植物的进化过程中被保留下来，但种子植物还通过腺苷酸ADP/ATP的异戊烯化重新合成了游离细胞分裂素。本课题旨在(1)为苔藓细胞分裂素生物合成的trna依赖途径的专一性提供明确的证据；(2)为trna依赖的细胞分裂素生物合成在基因调控水平上的调控以及tRNA-IPT性质和底物有效性提供基础信息。这一目标将通过tRNA-IPT基因敲除植株和tRNA-IPT过表达物的产生来实现。转录研究将把tRNA-IPT表达的定位与细胞分裂素生物合成/活性的拓扑结构联系起来。详细描述trna的转录和腺嘌呤37-异戊烯化将有助于了解trna介导的细胞分裂素生物合成的功能模式，有助于种子植物的生长控制。

For the moss Physcomitrella patens we collected evidence suggesting that in this model organism the plant hormones cytokinins (isopentenyl-derivatives of adenine), in contrast to seed plants, originate exclusively from tRNA. We therefore assume that in early steps of land plant evolution the isopentenylation of tRNA, catalysed by tRNA-isopentenyltransfrases (tRNA-IPTs), took over the function of providing precursors for free cytokinins acting as plant hormones. This tRNA-IPT mediated pathway of cytokinin biosynthesis was preserved during the evolution of seed plants, however seed plants additionally developed the de novo synthesis of free cytokinins via isopentenylation of the adenylates ADP/ATP. The proposed project aims (1) to establish the unequivocal proof for the exclusivity of the tRNA-dependent pathway of cytokinin biosynthesis in moss, (2) to provide basic information on the regulation of the tRNAdependent cytokinin biosynthesis on the levels of gene regulation as well as tRNA-IPT properties and substrate availability. The aims will be achieved by the generation of tRNA-IPT gene knockout plants and tRNA-IPT overexpressors. Transcriptional studies will correlate the localisation of tRNA-IPT expression with the topology of cytokinin biosynthesis/activity. A detailed description of transcription and adenine37- isopentenylation of tRNAs will help to understand the mode of function of tRNA-mediated cytokinin biosynthesis, contributing to growth control also in seed plants.