Knotted1-like homeobox genes are expressed during apple tree (Malus domestica [L.] Borkh) growth and development

Apple (Malus domestica [L.] Borkh) cDNA clones encoding two distinct but very similar kn1-like homeobox gene class 1 homologues (KNAP1 and KNAP2) were isolated using a fragment amplified with degenerated primers as a probe. A fragment corresponding to the homeodomain region of KNAP1 was used to isolate a cDNA (KNAP3) belonging to the kn1-like homeobox gene class 2. These probes were used to detect corresponding gene copies in apple genomic DNA digests, together with other putative members of an apple kn1-like homeobox gene family. The kn1-like homeobox gene probes were also used to detect corresponding messenger accumulation levels in various organs of an apple tree. Transcripts corresponding to KNAP1 and KNAP2 genes appeared to be absent from leaves or floral organs, but they accumulate in tissue samples from elongated parts of the stem. In contrast, KNAP3 mRNAs accumulate at detectable levels in a wider range of both vegetative and reproductive organs.