Functional analysis of retrotransposons in pea

The 5'-upstream regions of the plant active defense genes in pea (PSPAL2 and PSCHS1) exhibit significant nucleotide sequence identity to part of a copia-type retrotransposon. To characterize the retrotransposon in pea putative reverse transcriptase sequences (Psr) were amplified by PCR from cDNA prepared from protoplasts derived from pea suspension cultured cells. Psr genes can be classified into at least eight subgroups (A-H) according to their nucleotide sequence similarities. A subgroup PsrC was induced by the treatment of etiolated pea epicotyls with fungal elicitor within 30 min but was hardly induced by protoplasting of pea suspension cultured cells, whereas subgroups of PsrA and PsrB were highly induced by protoplasting. Interestingly, the retrotransposon sequence present at the 5'-upstream region of PSCHS1 which was induced by the treatment with fungal elicitor belonged to subgroup PsrC. The retrotransposon might play an important role in reorganization of the genes and optimization of the gene expression in response to various environmental stimuli such as an attack by phytopathogens or protoplasting.