Maternal Effect on Embryogenesis in Tobacco Overexpressing Rice Phytochrome A*

Abstract

When analyzing tobacco lines overexpressing various types of rice phytochrome A, we observed seedlings with fused cotyledons. Phytochrome A is a member of the phytochrome family of plant red/far‐red absorbing photoreceptors. Reciprocal crossings with wild‐type tobacco indicated that this abnormal phenotype was maternally inherited. Mother plants that were expected to produce abnormal seedlings, were raised under different conditions and seeds collected separately from individual capsules. The frequency of abnormal seedlings increased in seeds from later flowers but decreased when mother plants were raised under continuous white light. The interaction of the overexpressed phytochrome A proteins with endogenous plant hormones might be responsible for cotyledon fusion. The abnormal phenotype could partially be recovered by application of gibberellic acid to intact flowers at the time of pollination. In contrast, the synthetic auxin NAA slightly enhanced the degree of cotyledon fusion. Even wild‐type tobacco seedlings exhibited partial fusion of cotyledons if flowers were treated with 2,4‐D and occasionally the shoot apex was replaced by a second root. Application of GA3 to the flowers, in contrast, impaired the development of the radicule. These observations are discussed with respect to maternal effects in plant embryogenesis.

The CUP-SHAPED COTYLEDON3 Gene Is Required for Boundary and Shoot Meristem Formation in Arabidopsis

“…The SAM appears within the boundary, and failure to correctly establish the boundary correlates with failure to establish the SAM in plants with reduced CUC3, CUC1, CUC2, and/or STM function. Interestingly, tobacco seedlings with fused cotyledons resulting from the overexpression of phytochrome A also often lack a SAM (Emmler and Schäfer, 1997). Thus, the establishment of a boundary that contains cells with low proliferation and/or differentiation rates apparently is required for the establishment and/or maintenance of the shoot meristem.…”

The Arabidopsis SERRATE Gene Encodes a Zinc-Finger Protein Required for Normal Shoot Development

“…The embryo's dependence on SE activity for proper cotyledon initiation is interesting, and similar maternal control over plant embryo patterning has only previously been observed for the Arabidopsis sin1-2 mutant and transgenic tobacco plants overexpressing the oat phyA gene (Ray et al, 1996;Emmler and Schäfer, 1997). Given the presence of a haploid gametophyte generation between diploid sporophyte generations, maternal effects on plant embryo development are paradoxical because the embryo is isolated both spatially (by the endosperm) and mitotically (during megagametophyte development) from diploid maternal tissue.…”