Investigating the Link Between Growth and Pattern in the Arabidopsis Embryo

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Shoot and root apical meristems develop at opposite poles of the globular plant embryo. Despite much effort to obtain them, mutants altered in basic aspects of early development, such as the development of polarity along the shoot/root axis, have been elusive in angiosperm plants. This investigator hypothesizes that this is because alterations in embryo polarity also result in growth arrest and that the relevant mutants are therefore to be found among the much larger class of embryonic lethal/arrest mutants. Mutants in which shoot fates are transformed to root fates (double root embryos) or in which root fates are transformed into shoot fates (double shoot embryos) could arrest growth during embryogenesis. Support for this idea is found in the analysis of embryos homozygous for the topless-1 (tpl-1) mutation. The temperature sensitive tpl-1 mutation causes a high rate of shoot to root transformation at restrictive temperature. Among tpl-1 mutant embryos grown at restrictive temperature is a small class of arrested embryos that express root specific markers throughout the globular stage embryo (i.e., in both presumptive root and shoot poles) To test this hypothesis, Dr. Barton proposes to screen embryonic lethal/arrest mutants for the altered expression of a shoot pole specific marker (an STM reporter gene). Candidate mutants will then be analyzed with additional root and shoot specific markers to determine if they truly result in a polarity defect. In addition to this general screen, the PI will perform a more targeted screen for strong, non-temperature sensitive alleles of TPL. This screen is designed to test the hypothesis that a stronger allele of TPL will result in a more penetrant shoot to root transformation with a concomitant increase in the proportion of arrested embryos. The research described in this POWRE grant will make it possible for the PI to pursue a line of exploratory research that, if successful, should result in the isolation and characterization of mutants in the development of embryonic polarity, a fundamental event in early plant development.