Expression of a human tRNA isopentenyltransferase in tobacco reveals a developmental role for tRNA isopentenyladenosine

Multi-faceted nature of the tRNA isopentenyltransferase

Transfer RNA isopentenylation an adenine 37 position (A37) is a universal modification known in prokaryotes and eukaryotes. A set of highly homologous enzymes catalyse a series of reactions, leading to tRNA modifications, aimed to increase adaptation to environmental condition through the control of translation efficiency and reading frame maintenance. Transfer RNA-isopentenylation-related (TI-related) functions are well studied in bacteria, mitochondria of yeast and human, but completely unexplored in plants. Transfer RNA-isopentenylation-unrelated (TI-unrelated) functions participate in adaptation to environmental stresses via the regulation of sterol metabolism, gene silencing/suppression and amyloid fibrils formation. TI-unrelated functions are mostly studied in yeast. Finally, the degradation of A37-modified tRNA releases a set of bioactive compounds known as cis-cytokinins. Although all organisms are able to produce cis-cytokinins, its physiological role is still a matter of debates. For several species of bacteria and fungi, cis-cytokinins are known to play a crucial role in pathogenesis. In mammalian and human models cis-cytokinins have tumour-suppressing and anti-inflammation effects. This review aims to summarise current knowledge of the TI-related and TI-unrelated functions and main bioactive by-products of isopentenylated tRNA degradation.

Genetic engineering of cytokinin metabolism: prospective way to improve agricultural traits of crop plants

Cytokinins (CKs) are ubiquitous phytohormones that participate in development, morphogenesis and many physiological processes throughout plant kingdom. In higher plants, mutants and transgenic cells and tissues with altered activity of CK metabolic enzymes or perception machinery, have highlighted their crucial involvement in different agriculturally important traits, such as productivity, increased tolerance to various stresses and overall plant morphology. Furthermore, recent precise metabolomic analyses have elucidated the specific occurrence and distinct functions of different CK types in various plant species. Thus, smooth manipulation of active CK levels in a spatial and temporal way could be a very potent tool for plant biotechnology in the future. This review summarises recent advances in cytokinin research ranging from transgenic alteration of CK biosynthetic, degradation and glucosylation activities and CK perception to detailed elucidation of molecular processes, in which CKs work as a trigger in model plants. The first attempts to improve the quality of crop plants, focused on cereals are discussed, together with proposed mechanism of action of the responses involved.