1. A process of endowing a plant or plant cells with a trait of interest by expressing an RNA sequence of interest, said process comprising: transforming plant cells or cells of said plant with a first vector and a second vector and selecting cells endowed with said trait of interest, wherein said first vector contains a first nucleotide sequence with a first segment coding, in 5′ to 3′ direction, for (i) a 5′ part of said RNA sequence of interest and (ii) a 5′ part of an intron; and said second vector contains a second nucleotide sequence with a second segment coding, in 5′ to 3′ direction, for (i) a 3′ part of an intron and (ii) a 3′ part of said RNA sequence of interest; wherein said 5′ part of the intron and said 3′ part of the intron leads to the formation of said RNA sequence of interest by splicing of a primary transcript containing said 5′ part of said RNA sequence of interest, said 5′ part of the intron, said 3′ part of the intron, and said 3′ part of said RNA sequence of interest, thereby forming said RNA sequence of interest as a secondary transcript, wherein said primary transcript is transcribed from a functional transcription unit comprising said first nucleotide sequence and said second nucleotide sequence, and wherein said second vector is devoid of a transcriptional promoter for transcribing said 3′ part of the intron and said 3′ part of said RNA sequence of interest.