Leaf-specific suppression of deoxyhypusine synthase in Arabidopsis thaliana enhances growth without negative pleiotropic effects.

Deoxyhypusine synthase (DHS) mediates the first of two enzymatic reactions required for the post-translational activation of eukaryotic translation initiation factor 5A (eIF5A), which in turn is thought to facilitate translation of specific mRNAs. Analyses of GUS activity in transgenic Arabidopsis plants expressing the GUS reporter gene under regulation of the promoter for AtDHS revealed that the expression of DHS changes both spatially and temporally as development progresses. In particular, DHS is expressed not only in rosette leaves, but also in the anthers of developing flowers. To determine the role of DHS in leaves, transgenic plants in which DHS was selectively suppressed in rosettes of Arabidopsis plants were prepared. This was achieved by expressing AtDHS 3'-UTR cDNA as a transgene under regulation of the promoter for AtRbcS2, a gene encoding the small subunit of Rubisco. The dominant phenotypic traits of the DHS-suppressed plants proved to be a dramatic enhancement of both vegetative and reproductive growth. As well, the onset of leaf senescence in the DHS-suppressed plants was delayed by approximately 1 week, but there was no change in the timing of bolting. In addition, there was no evidence for the negative pleiotropic effects, including stunted reproductive growth and reduced seed yield, noted previously for transgenic plants in which DHS was constitutively suppressed. The results indicate that DHS plays a pivotal role in both growth and senescence.