Molecular and physiological characterisation of an insertion mutant in the ARR21 putative response regulator gene from Arabidopsis thaliana

In our search for insertion mutants of Arabidopsis response regulator (ARR) genes, we identified a candidate for an ARR21 dSpm transposon insertion line in the SLAT collection by searching the SINS sequence database. Molecular characterisation of this line revealed that the transposon is integrated as a single copy 1727 bases downstream of the ATG signal, within the third intron of the ARR21 gene. The transposon insertion segregated in a Mendelian fashion from heterozygous plants that were allowed to self-pollinate. RT-PCR-based expression analysis showed that ARR21 transcript predominantly accumulates in siliques. In contrast, the full-length ARR21 transcript was not detectable in the ARR21 transposon insertion line, indicating that it harbours an insertion of dSpm transposon in the ARR21 gene. The ARR21 insertion mutant (arr21-1) was subjected to several physiological tests for a possible insertion-linked phenotype. However, our results revealed that the insertion in the ARR21 gene did not cause any alterations in viability and fertility, flowering time, sensitivity to ethylene, cytokinin or red light. We discuss these results in the light of recent findings about the function of the other members of the response regulator gene family of Arabidopsis.