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.