Fasciation, from the Latin, fascis, meaning bundle, is a process that describes variations in plant form resulting from abnormal growth of part of the plant body. Usually fasciation is recognized by an enlargement and flattening of the stem, resulting from proliferation at the shoot apex. In principle, this could occur by a number of mechanisms operating in the central or peripheral zone of the shoot apical meristem:
(i) by an increase in the rate of cell division in the central and/or peripheral zone, or
(ii) by a delay in the transition from central to peripheral zone identity, resulting in an accumulation of central zone cells, or
(iii) by a delay in the incorporation of peripheral zone cells into primordia, resulting in an enlargement of the peripheral zone.
Heritable ear fasciation in maize has been known for a long time (Weatherwax, P., 1935, The American Midland Naturalist 16:1-71). Several years ago we reported a new mutant of maize called fasciated ear (fae) (Hake, S. and Veit, B., MNL 62:2, 1988). Mutant plants had enlarged and branched ears resulting from fasciation of the ear inflorescence meristem. Following introgression into the B73 inbred line, we noticed that the phenotype was modified and the ear branches were smaller and coming from the base of the ear. This phenotype resembled the ears of ramosa3 (ra3) plants, and crossing these mutants together showed that they fail to complement. Subsequent F2 analysis indicated that fae and ra3 are indeed allelic, and we have therefore renamed this allele ra3-fae1.
I (DJ) am characterizing new recessive fasciated ear mutants, preliminarily named fae2 and fae3, that were gifts from Paul Chomet (Dekalb Plant Genetics) and maize cooperators in Krasnodar, Russia, respectively (Fig. 1). In addition, the compact plant2 (ct2) mutation from the Maize Stock Center has severely fasciated ears as well as a thick tassel phenotype. A second isolate of ct2; ct2-rd3, from the Stock Center, also shows severely fasciated ears.
The compact plant1 mutant is also described in the Maize Newsletter gene list as having furcated (branched) ears, but in my experience ct1 plants have normal ears, and their description may have been confused with ct2. Phenotypic and molecular characterization of the fasciated ear mutants is in progress.
Figure 1. Fasciated ear mutants of maize.
A. Normal mature ears showing straight rows of kernels. The ears taper towards the tip (to the right of this ear).
B. ra3-fae1 mutant ears. The upper ear is fasciated and the tip is broad and flattened and the rows of kernels are irregular. The ear below from a different family does not show the fasciated phenotype but has branches at the base (arrows). These are axillary inflorescence branches that sometimes bear kernels.
C. fae2 mutant ears. The upper ear shows broadening and flattening of the tip of the ear and the rows of kernels are irregular. The lower ear has been sparsely pollinated and shows the cob structure, typically this mutation shows line fasciation where the apex is flattened and extended into a curving line.
D. fae3 mutant ears. The tip of these ears is broad and branched, and typically undergoes splitting and ring fasciation to form an ear that is hollow on the inside.
E. ct2 mutant ears. These ears show flattening and broadening of the tip, somewhat similar to fae2. The lower ear is not pollinated and shows the distorted shape of the cob.
F. Immature normal ear, with the silks removed to show the narrow tapering tip and the regular rows of florets.
G. Immature fae2 ears, showing flattening and branching of the tip of the ear.
H. Immature fae3 mutant ears, in this case the tips of the ear are broader in all directions rather than being flattened.
I. Immature ct2 ear showing severe enlargement and flattening
at the tip. This mutation also causes broadening of the central spike of
the tassel, shown to the right.
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