A role for KNOX genes in the development of reproductive organs of Helianthus.

KNOTTED1-like homeobox (KNOX) genes act in the shoot apical meristem (SAM) to provide an uncommitted population of cells for organogenic programs. In addition to playing a role in SAM function and leaf morphology, there is also evidence of the involvement of KNOX genes in some features of flower development. The expression pattern of HtKNOT1, a class I KNOX gene, in inflorescence meristems, floral meristems and floral organs of two related species, Helianthus tuberosus and H. annuus strengthens this view. HtKNOT1 mRNAs have been detected in the inflorescence and floral meristems as well within lateral organ primordia (i.e. floral bracts, petals, stamens and carpels). In more differentiated flowers, the expression of HtKNOT1 was restricted to developing ovules and pollen. Class I KNOX genes may play a dual role being required to maintain the meristem initials as well as initiating differentiation and/or conferring new cell identity. In the genus Helianthus, some KNOX genes could cooperate at the floral level with additional factors that more specifically control floral organs and pollen development.