Late embryo‐defective mutants of Arabidopsis

Abstract

The embryo-defective (emb) mutants of Arabidopsis constitute a large and diverse group of mutants disrupted in a broad range of embryonic processes, including morphogenesis, cell differentiation, and maturation programs. This report describes a subset of these mutants, the late embryo defectives, which develop beyond the globular stage of embryogenesis but fail to complete normal morphogenesis. A representative sample of 12 late mutants was chosen for this study, patterns of morphogenesis were characterized, the germination potential of mutant seeds was investigated, and additional mutant alleles within the collection were identified. Morphological defects in mutant embryos became apparent during the heart stage of development, when embryos normally begin the rapid cell division and expansion required for the completion of morphogenesis. Despite their morphological abnormalities, mutant embryos often germinated from dry seed, demonstrating that genetic programs required for the establishment of desiccation tolerance remained intact. Mutant seedlings displayed a wide range of developmental abnormalities, including altered morphology, lack of pigmentation, dwarfism, and disorganized vegetative growth. One late mutant was found to be allelic to an early embryo defective that arrests at the globular stage. These results suggest that a number of late EM5 genes encode basic cellular and metabolic functions needed for cell division, enlargement, and embryonic growth. The rapid growth and metabolic changes that occur at the heart stage may present a barrier to normal development in the late mutants, resulting in altered embryo morphology and other developmental defects. It is proposed that many Arubidopsis mutants with abnormal embryo and seedling morphology are not defective in the regulation of pattern formation or morphogenesis, but rather in fundamental physiological and cellular processes required for the completion of normal growth and development. o 1995 Witey-iiss, inc.

The Expression of Small Heat Shock Proteins in Seeds Responds to Discrete Developmental Signals and Suggests a General Protective Role in Desiccation Tolerance

“…We then tested sHSP expression in mutants of other transcriptional activators required for seed development and desiccation tolerance, fus3-3 Luerssen et al, 1998) and lec1-2 (West et al, 1994;Lotan et al, 1998), to determine if their effects were similar or different from that of abi3. Finally, we analyzed sHSP accumulation in an additional desiccation-intolerant mutant, line24 (K. Yamagishi and J. Harada, personal communication), and two desiccation-tolerant mutants with severe defects in embryogenesis, lec2-1 (Meinke et al, 1994) and emb266 (Vernon and Meinke, 1995). This expanded analysis of seed development mutants further supports a function for sHSPs in desiccation tolerance, and provides direct evidence that ABI3 is required for transcriptional activation of HSP17.4 in seeds.…”

TheTORMOZGene Encodes a Nucleolar Protein Required for Regulated Division Planes and Embryo Development inArabidopsis

“…Some embryo lethal mutants are able to be rescued if released from the developmental and physiological restrictions of the mother plant (Vernon and Meinke, 1995). To test this, mutant seed containing embryos were removed from sterilized siliques and grown on basal tissue culture media without hormones.…”

Identification of Genes Required for Embryo Development in Arabidopsis

“…Arabidopsis genes that are required for viability under normal conditions and cannot be passed to subsequent generations when disrupted are often considered to be essential. Problems arise when considering genes such as LEC1, where homozygous mutant seeds cannot survive desiccation but give rise to viable plants if germinated precociously (Meinke, 1992), and EMB genes with late terminal phenotypes, where mutant embryos may produce callus (Franzmann et al, 1989) and germinate to form abnormal seedlings (Vernon and Meinke, 1995). If we define essential as required to complete the life cycle under normal conditions, then many genes with knockout phenotypes affecting flower development would fall into the essential class despite the absence of reduced viability.…”