Gene duplication at the <i>Fascicled ear1</i> locus controls the fate of inflorescence meristem cells in maize

Abstract

Plant meristems are self-renewing groups of pluripotent stem cells that produce lateral organs in a stereotypical pattern. Of interest is how the radially symmetrical meristem produces laminar lateral organs. Both the male and female inflorescence meristems of the dominant <i>Fascicled ear</i> (<i>Fas1</i>) mutant fail to grow as a single point and instead show deep branching. Positional cloning of two independent <i>Fas1</i> alleles identified an ∼160 kb region containing two floral genes, the <i>MADS-box</i> gene, <i>zmm8</i>, and the <i>YABBY</i> gene, <i>drooping leaf2</i> (<i>drl2</i>). Both genes are duplicated within the <i>Fas1</i> locus and spatiotemporally misexpressed in the mutant inflorescence meristems. Increased <i>zmm8</i> expression alone does not affect inflorescence development; however, combined misexpression of <i>zmm8</i>, <i>drl2</i>, and their syntenic paralogs <i>zmm14</i> and <i>drl1</i>, perturbs meristem organization. We hypothesize that misexpression of the floral genes in the inflorescence and their potential interaction cause ectopic activation of a laminar program, thereby disrupting signaling necessary for maintenance of radially symmetrical inflorescence meristems. Consistent with this hypothesis, RNA sequencing and in situ analysis reveal altered expression patterns of genes that define distinct zones of the meristem and developing leaf. Our findings highlight the importance of strict spatiotemporal patterns of expression for both <i>zmm8</i> and <i>drl2</i> and provide an example of phenotypes arising from tandem gene duplications.