CONTEXT

Plant mitochondrial genetics determines or contributes to a number of agronomically important traits, as for instance cytoplasmic male sterility. On the other hand, plant mitochondria have large genomes, with numerous unassigned regions, and complex genetic processes. Mastering the genetic system in plant mitochondria is thus of wide interest and has many applications. Unfortunately, the current conventional methods do not enable to transform these organelles, so that it is difficult to generate valuable mitochondrially-driven traits and to identify new mitochondrial genes or regulation functions.

Based on the natural transfer RNA (tRNA) import pathway of plant mitochondria, the inventors have developed the use of a tRNA mimic as a vector to drive into the organelles RNAs of interest expressed in the nucleus. The inventors have then designed a sequence comprising a trans-cleaving hammerhead ribozyme attached to a tRNA mimic through a special linker. The ribozyme activity of this chimeric RNA has been validated in vitro. Subsequent expression in plant cell suspensions and in whole plants from an inducible nuclear transgene demonstrated the in vivo import of the chimeric RNA into mitochondria and the specific cleavage of the target RNA in the organelles, yielding the first directed knockdown of a mitochondrial RNA in plants.

As a whole, this invention is a new method to genetically manipulate mitochondria in plant cells, using nuclear expression and organellar import of chimeric catalytic RNAs.