Abstract
The shoot apical meristem (SAM) is an indeterminate structure that maintains itself, and initiates all above ground organs throughout the life cycle. Class I Knotted1-like homeobox (KNOX) genes are specifically expressed in the SAM, and maintain its indeterminacy in flowering plants. Despite the indispensable roles of KNOX genes for SAM formation and maintenance, virtually nothing is known about the mechanisms how positively regulate their expression. By genetic analyses, we found that the expression of KNOX genes depends on the function of themselves. OSH1 positively regulates the expression of all KNOX genes in a direct manner through evolutionarily conserved cis-elements. Furthermore, we show that these cis elements on OSH1 loci are essential for its expression and SAM maintenance. Taking together, the maintenance mechanism of the indeterminate state mediated by positive autoregulation of a KNOX gene emerges as a novel mechanism of self-maintenance system of the SAM that ensures the unique body plan of flowering plants.
