Isolation and characterization of the KNAT6 homeobox gene in Arabidopsis thaliana
Class 1 KNOX genes have been demonstrated to play roles in the maintenance of the shoot apical merlstem in a variety of plant species. Although the shoot and root systems differ in the way in which lateral organs are initiated, it was proposed that KNOX genes may also function in some aspect of the regulation of the root apical or lateral root meristems. This work describes the Isolation and characterisation of KNAT6, a member of this family in the model plant Arabidopsis thaliana. KNAT6 cDNA was isolated from NAA-treated root tissue. Two isoforms were identified, which differ by two amino acids in the conserved MEINOX domain of the predicted protein. The KNAT6 transcript is detectable in seedlings between 3 and 12 days after germination. The KNAT6 promoter is active in the phloem poles of the main root in Arabidopsis, especially at the bases of newly emerged lateral roots. Promoter activity is downregulated by cytokinin and the pattern of expression alters on treatment with the synthetic auxin analogue NAA. Overexpression studies revealed that the shorter and more abundant KNAT6 cDNA isoform causes a lobed leaf phenotype when it is over expressed, a phenotype similar to that seen on overexpression of other class 1 KNOX genes in Arabidopsis. The longer and less abundant cDNA isoform does not cause this phenotype, indicating that there is a functional difference between the two predicted proteins. Preliminary analysis of plants carrying RNAi constructs indicates that lateral roots are initiated closer to the root tip than in wild type plants. Taken together, and in the context of the literature, these results suggest that KNAT6 may be involved In control of lateral root development and root architecture in Arabidopsis.