ALBANY, CALIFORNIA
USDA Plant Gene Expression Center
BERKELEY, CALIFORNIA
University of California

A gene required for floral and inflorescence meristem determinacy
 --Laudencia-Chingcuanco, D; Hake, S

A recessive mutation, designated not under control (nuc), was identified from our Ac/Ds field in the summer of 1995. nuc plants are recognized in the field by the absence of protruding silks from otherwise normal looking ears. De-husked ears reveal florets with proliferous material at the center of the pistil. Upon closer inspection, the mutation appears to disrupt a gene required for the specification of a determinate floral meristem. In the female flowers, the floral apex, which is normally consumed in the formation of the gynoecium (see figure, wt) remains indeterminate. After formation of the carpels, an unorganized mass of pistillate tissue or an inflorescence-like, branching meristem is produced at the center of the flower (figure, nuc). The lower floret, which ultimately aborts, displays the same phenotype as the upper floret. Pollinated nuc ears failed to produce any kernels. In the tassel, additional male flowers form at the position of the aborted pistil. Occasionally, a nucellar-like mass is found at the center of these ectopic staminate flowers. nuc inflorescences also have extra spikelets and florets. In the ear, an extra spikelet forms between the spikelet pair. In the tassel, up to 6 extra spikelet pairs are produced after the pedicellate spikelet. Sometimes, an extra staminate flower is found between the two flowers in the spikelet.

This transformation from flower to inflorescence shoot meristem has also been reported to occur in several species under particular growth conditions (Battey and Lyndon, Bot. Rev. 56:162, 1990; Okamura et al., PNAS 93:13831, 1996), indicating that floral meristem determinacy is labile. Because nuc is a single gene that is required to prevent indeterminacy within the flower, we have a unique opportunity to explore the regulation of determinacy in flowers.

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