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

对于短柄苔藓，我们收集的证据表明，在这个模式生物中，与种子植物相比，植物激素细胞分裂素(腺嘌呤的异戊烯基衍生物)完全来自tRNA。因此，我们推测，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异戊烯基化起到了作为植物激素的游离细胞分裂素前体的作用。这种tRNA-IPT介导的细胞分裂素生物合成途径在种子植物进化过程中被保留下来，但种子植物还通过腺苷ADP/ATP的异戊烯基化来发展游离细胞分裂素的从头合成。该项目的目的是(1)明确证明苔藓中依赖tRNA的细胞分裂素生物合成途径的排他性，(2)为依赖tRNA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的性质和底物的可获得性提供基本信息。这些目的将通过产生tRNA-ipt基因敲除植株和tRNA-ipt过表达载体来实现。转录研究将tRNA-IPT表达的定位与细胞分裂素生物合成/活性的拓扑结构相关联。对tRNAs转录和腺苷37-异戊烯基化的详细描述将有助于理解tRNA介导的细胞分裂素生物合成的功能模式，也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.