3 KNOTTED1-LIKE HOMEOBOX GENES IN ARABIDOPSIS

Five arabidopsis kn1-like homeobox genes were cloned through low-strin gency screening of Arabidopsis cDNA libraries with the kn1 homeobox fr om maize. These five genes were named KNAT1-5 (for kn1-like Arabidopsi s thaliana). An analysis of KNAT1 and 2 has been presented previously [19]. Here we present an analysis of the genes KNAT3, 4 and 5. On the basis of sequence and expression patterns, these three genes belong to the class II subfamily of kn1-like homeobox genes [16]. Low-stringenc y Southern analysis suggests several additional members of the class I I genes exist in the Arabidopsis genome. The predicted amino acid sequ ences of the three genes share extensive homology outside of the homeo domain, including 84% between KNAT3 and KNAT4. Northern analysis shows that although all three genes are expressed in all tissues examined, the level of KNAT3 RNA is highest in young siliques, inflorescences an d roots, KNAT4 RNA level is strongest in leaves and young siliques, an d KNAT5 RNA level is highest in roots. The specificity of these patter ns was confirmed by RNA fingerprint analysis. KNAT3 and 4 are light-re gulated as they show reduced expression in etiolated seedlings and als o in hy3, cop1 and det1 mutant backgrounds.