reverse germ orientation 1 mutants make three florets per spikelet
--Kaplinsky, NK, Freeling, M

Reverse germ orientation 1 - R (rgo1 -R) is a previously described mutant where the embryo faces the base of the ear, the reverse of the normal kernel orientation (Sachan and Sarkar, MNL 52:119-120, 1978). Similar recessive phenotypes have been explained by a reversal of normal development; the lower floret of a spikelet develops as opposed to the upper floret (reviewed in Jackson, MNL 70:66, 1996). It appears that the reverse germ phenotype is actually due to the development of one extra floret per spikelet (pers. comm. G. Chuck and R. Kerstetter). In the tassel, three florets and nine anthers are often, but not always found in rgo1 plants (Fig. 1). Mutant ears elaborate three florets per spikelet , as opposed to two in wild type (Fig. 2). This suggests that rgo1 may be involved in regulating the transition of spikelet meristems to floret meristems.

Figure 1. rgo1 tassel spikelet showing the development of three florets, producing a total of nine anthers per spikelet.

Figure 2. SEM of developing rgo1 ear. The left panel shows the ear. The top right panel shows three floret meristems developing on one spikelet. The lower right panel shows the third floret developing, with the anther primordia reversed relative to their normal orientation.

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