This domain is required for the nuclear localisation of these proteins (PUBMED:11352458). All of these proteins are members of the Tale/Knox homeodomain family, a subfamily within homeobox SM00389.
Homeobox genes, which encode homeodomain (HD) transcription factors, are known to be key regulators of both plant and animal development. In plants homeobox genes are divided into several groups by sequences, one of which is the KNOX (for knotted1-type homeobox) family. Proteins of this family share other conserved domains, the KNOX domain and ELK domain, which is immediately upstream of the HD. The ELK domain spans ~21 amino acids and was dubbed for a highly conserved series of Glu, Leu, and Lys amino acids. It could function as a nuclear localization signal. The ELK domain also is considered to act as a protein-protein interaction domain, but the precise role of this domain has not been determined [ (PUBMED:7866030) (PUBMED:10449577) (PUBMED:11549765) (PUBMED:12034492) ].
The ELK domain contains repeating hydrophobic residues and has been predicted to form an amphipathic helix [ (PUBMED:7866030) ].
Expression of a class 1 knotted1-like homeobox gene is down-regulated in peacompound leaf primordia.
Plant Mol Biol. 2001; 45: 387-98
Display abstract
Differences in knotted1-like (knox) gene expression may account for some of thediversity of leaf forms seen in nature. Class 1 knox genes are expressed in thecompound leaf primordia of tomato but not in the simple leaf primordia of a rangeof species examined so far. In order to test the hypothesis that all compoundleaves differ from simple leaves in this way, we isolated a class 1 knox cDNAfrom pea, Pskn1 (Pisum sativum knotted1) and examined its expression pattern. Theencoded homeodomain of Pskn1 shares 88% identical residues with KNOTTED1 frommaize and an adjacent ELK domain is present. The protein sequence of PSKN1 is 69%identical to TKN2, its nearest related sequence in tomato. Unlike TKn2, Pskn1 wasnot expressed in newly initiated compound leaves. The expression pattern of Pskn1resembled those of other class 1 knox genes described in maize and Arabidopsis.Transcripts were detected in the shoot apical meristem and developing vasculatureof the vegetative shoot, but expression was not detected in newly initiated anddeveloping compound leaf primordia. The same pattern of expression was observedin the afila mutant, which is characterised by highly ramified compound leaves.Our results suggest that tomato and pea use different developmental processes in the generation of their compound leaves.
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