Knotted1-like genes are strongly expressed in differentiated cell types in sunflower

Knotted1-like genes constitute a family of genes whose products are transcription factors involved in several aspects of plant development. In most species, these genes are expressed primarily in meristematic cells and are switched off as leaves develop. In this paper, the expression patterns of three kn1-like genes from sunflower (Helianthus annuus L.) are described. Northern blot experiments indicated that these genes are expressed at different levels in several organs of the plant, including flowers, leaves, stems, roots, and embryos. Notably, one of these genes, named HAKN1, was also highly expressed in leaves and roots. Using in situ hybridization, expression was detected in parenchymatic cells from leaf veins, petiole and lamina, and also in stem and root. Enhanced expression in phloem was also evident in both leaves and stem. Another, HAKN2, showed preferential expression in stem, specifically in fascicular and interfascicular cambium and phloem. In flowers, both genes are expressed throughout inflorescence and floral meristems and in developing organ primordia. Strong expression of HAKN1 in developing involucral bracts was also observed. The results show the existence of some differences in expression patterns of kn1-like genes in sunflower with respect to other plants. It is proposed that cell- and species-specific factors are involved in determining the developmental responses of plant cells to the expression of kn1-like genes.