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. 1997 Sep 16;94(19):10209-14.
doi: 10.1073/pnas.94.19.10209.

Mutations of Arabidopsis thaliana that transform leaves into cotyledons

L J Conway  1 , R S Poethig
Affiliations

Mutations of Arabidopsis thaliana that transform leaves into cotyledons

L J Conway et al. Proc Natl Acad Sci U S A. .

Abstract

We describe mutations of three genes in Arabidopsis thaliana-extra cotyledon1 (xtc1), extra cotyledon2 (xtc2), and altered meristem programming1 (amp1)-that transform leaves into cotyledons. In all three of these mutations, this transformation is associated with a change in the timing of events in embryogenesis. xtc1 and xtc2 delay the morphogenesis of the embryo proper at the globular-to-heart transition but permit the shoot apex to develop to an unusually advanced stage late in embryogenesis. Both mutations have little or no effect on seed maturation and do not affect the viability of the shoot or the rate of leaf initiation after germination. amp1 perturbs the pattern of cell division at an early globular stage, dramatically increases the size of the shoot apex and, like xtc1 and xtc2, produces enlarged leaf primordia during seed development. These unusual phenotypes suggest that these genes play important regulatory roles in embryogenesis and demonstrate that the development of the shoot apical meristem and the development of the embryo proper are regulated by independent processes that must be temporally coordinated to ensure normal organ identity.

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Figures

Figure 1
Figure 1
The phenotype of (a) wild-type, (b) xtc1, (c) xtc2, and (d) amp1(pt) seedlings 2 weeks after germination. Leaves 1 and 2 are at the top and bottom of each figure. The true cotyledons, which are oriented horizontally, are smaller in mutant than in wild-type plants and are hidden by leaf primordia in b, c, and d.
Figure 2
Figure 2
The morphology of a (a) cotyledon and (b) first leaf of a wild-type plant, and the first leaf of (c) xtc1, (d) xtc2, and (e) amp1(pt) seedlings. The first leaves of mutant plants have few or no trichomes, and they have a simple venation pattern like that of cotyledons.
Figure 3
Figure 3
Electron micrographs of (a) a wild-type cotyledon and (b) a wild-type first leaf primordium and the first leaf primordia of (c) xtc1, (d) xtc2, and (e) amp1(pt) seedlings 2 days after imbibition. Wild-type leaf primordia are almost completely devoid of storage products, whereas cotyledon-like leaf primordia have large numbers of lipid bodies, starch grains, and the remnants of storage protein bodies. The cotyledon in a is at a much more advanced stage of development than the leaf primordia. (Scale bar = 5 μm.)
Figure 4
Figure 4
Wild-type and mutant embryos at 4 days (a, b, c, and d), 5 days (e, f, g, and h), 6 days (i, j, k, and l) and 10 days (m, n, o, and p) after pollination. (a, e, i, and m) Wild type. (b, f, j, and n) xtc1. (c, g, k, and o) xtc2. (d, h, l, and p) amp1(pt). lf, leaf primordium. (Scale bar: a–l = 50 μm; m–p = 100 μm.)
Figure 5
Figure 5
The first leaf of (a) amp1(pt)/amp1(pt), (b) amp1(pt)/amp1(pt); psd/psd, and (c) psd/psd mutant plants. The double mutant leaf in b resembles a normal first leaf in having well developed trichomes and a complex venation pattern.
Figure 6
Figure 6
Mature wild-type and mutant plants. (Left to Right) Ler, xtc1, xtc2, and amp1(pt).
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