Os04g0463500

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Annotated Information

Function

• 　TDD1 encodes a protein homologous to anthranilate synthase b-subunit, which catalyses the first step　of the Trp　biosynthesis pathway and functions upstream of Trp-dependent IAA biosynthesis.

Mutation

• The mature tdd1 embryo grows to more than 1.5 mm in length, which is slightly smaller than the wild-type (WT) embryo (Figure 2a,b). The growth rate of the mutant embryo is much lower than that of WT and the size of the mutant embryo at 5 days after pollination (DAP) is similar to that of the WT embryo at 3 DAP. At the early stages of embryogenesis, before organogenesis, the tdd1 embryo is morphologically indistinguishable from WT. Around 4 DAP or later, the tdd1 embryo can be distinguished from the WT embryo by the absence of both shoot and radicle in the mutant. Although the matured tdd1 embryo exhibits a simple internal structure, a cell-dense region usually forms around its center (arrowhead in Figure 2b) and a palisade-like cell layer, which may correspond to the epithelium layer, forms at its surface (Figure 2b, arrow and superimposed panel). The researchers examined the expression of two molecular markers, OSH1 and OsSCR, that are specifically expressed in the presumptive region of future shoot formation and the L2 layer of embryo, respectively. These two marker genes were expressed in the mutant embryos at the same places as in the WT embryos (Figure 2d,f). These results suggest that the tdd1 embryo succeeds in localization of the shoot region and in establishment of L2 layer identity and consequently succeeds in establishment of the basic pattern of the embryo. In contrast to severe defects in organ formation in the tdd1 embryo, the tdd1 endosperm develops normally, indicating that TDD1 is not involved in endosperm formation and development (Figure 2h compared with 2g). The growth of the mutant calli was slower than that of WT calli, which corresponds to the lower growth rate of the tdd1 embryo. When tdd1 calli were placed on regeneration medium, some of them produced adventitious leaves and shoots (Figure 2j).

Figure 2. Phenotypes of tdd1 embryos. (a, b) Median longitudinal sections of mature embryos of WT (a) and tdd1 (b). (a) Arrowhead and arrow indicate root apical meristem and shoot apical meristem, respectively. s, c and e indicate scutellum, coleoptile and epiblast, respectively. (b) Organless phenotype of tdd1 embryo. Inset shows a close-up view of an epithelium-like layer indicated by the arrow. A cell-dense region is indicated by the arrowhead. Bars = 200 lm. (c–f) in situ hybridization with the antisense RNA probe against OsSCR (c, d) and OSH1 (e, f). (c, e) WT embryos 3 DAP. (d, f) tdd1 embryos 5 DAP. Bars = 50 lm. (g, h) Mature seeds of WT (g) and tdd1 (h). Arrowheads indicate the embryos. No apparent difference was observed between the endosperms of the two genotypes. Bars = 2 mm. (i, j) Regenerated plants from calli of WT (i) and tdd1 (j). The regenerated plants of tdd1 can develop shoots and root. .

Expression

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Evolution

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Labs working on this gene

• Bioscience and Biotechnology Center, Nagoya University, Nagoya, Aichi 464-8601, Japan,
• Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan,
• Genome Resource Center, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan, and
• Graduate School of Agriculture and Life Sciences, University of Tokyo, Tokyo 113-8657, Japan