No abstract

A long-term goal of Arabidopsis research is to define the minimal gene set needed to produce a viable plant with a normal phenotype under diverse conditions. This will require both forward and reverse genetics along with novel strategies to characterize multigene families and redundant biochemical pathways. Here we describe an initial dataset of 250 EMB genes required for normal embryo development in Arabidopsis. This represents the first large-scale dataset of essential genes in a flowering plant. When compared with 550 genes with other knockout phenotypes, EMB genes are enriched for basal cellular functions, deficient in transcription factors and signaling components, have fewer paralogs, and are more likely to have counterparts among essential genes of yeast (Saccharomyces cerevisiae) and worm (Caenorhabditis elegans). EMB genes also represent a valuable source of plant-specific proteins with unknown functions required for growth and development. Analyzing such unknowns is a central objective of genomics efforts worldwide. We focus here on 34 confirmed EMB genes with unknown functions, demonstrate that expression of these genes is not embryo-specific, validate a strategy for identifying interacting proteins through complementation with epitope-tagged proteins, and discuss the value of EMB genes in identifying novel proteins associated with important plant processes. Based on sequence comparison with essential genes in other model eukaryotes, we identify 244 candidate EMB genes without paralogs that represent promising targets for reverse genetics. These candidates should facilitate the recovery of additional genes required for seed development.

In flowering plants, the egg develops within a haploid embryo sac (female gametophyte) that is encased within the pistil. The haploid pollen grain (male gametophyte) extends a pollen tube that carries two sperm cells within its cytoplasm to the embryo sac. This feat requires rapid, precisely guided, and highly polarized growth through, between, and on the surface of the cells of the stigma, style, and ovary. Pollen tube migration depends on a series of long-range signals from diploid female cells as well as a short-range attractant emitted by the embryo sac that guides the final stage of tube growth. We developed a genetic screen in Arabidopsis thaliana that tags mutant pollen with a cell-autonomous marker carried on an insertion element. We found 32 haploid-disrupting (hapless) mutations that define genes required for pollen grain development, pollen tube growth in the stigma and style, or pollen tube growth and guidance in the ovary. We also identified genomic DNA flanking the insertion element for eleven hap mutants and showed that hap1 disrupts AtMago, a gene whose ortholog is important for Drosophila cell polarity.