APETALA2 (AP2) plays a central role in the establishment of the floral meristem, the specification of floral organ identity, and the regulation of floral homeotic gene expression in Arabidopsis. We show here that in addition to its functions during flower development, AP2 activity is also required during seed development. We isolated the AP2 gene and found that it encodes a putative nuclear protein that is distinguished by an essential 68-amino acid repeated motif, the AP2 domain. Consistent with its genetic functions, we determined that AP2 is expressed at the RNA level in all four types of floral organs--sepals, petals, stamens, and carpels--and in developing ovules. Thus, AP2 gene transcription does not appear to be spatially restricted by the floral homeotic gene AGAMOUS as predicted by previous studies. We also found that AP2 is expressed at the RNA level in the inflorescence meristem and in nonfloral organs, including leaf and stem. Taken together, our results suggest that AP2 represents a new class of plant regulatory proteins that may play a general role in the control of Arabidopsis development.

Most of the transcription factors (TFs) responsible for controlling seed development are not yet known. To identify TF genes expressed at specific stages of seed development, including those unique to seeds, we used Affymetrix GeneChips to profile Arabidopsis genes active in seeds from fertilization through maturation and at other times of the plant life cycle. Seed gene sets were compared with those expressed in prefertilization ovules, germinating seedlings, and leaves, roots, stems, and floral buds of the mature plant. Most genes active in seeds are shared by all stages of seed development, although significant quantitative changes in gene activity occur. Each stage of seed development has a small gene set that is either specific at the level of the GeneChip or up-regulated with respect to genes active at other stages, including those that encode TFs. We identified 289 seed-specific genes, including 48 that encode TFs. Seven of the seed-specific TF genes are known regulators of seed development and include the LEAFY COTYLEDON ( LEC ) genes LEC1, LEC1-LIKE, LEC2 , and FUS3 . The rest represent different classes of TFs with unknown roles in seed development. Promoter-β -glucuronidase ( GUS ) fusion experiments and seed mRNA localization GeneChip datasets showed that the seed-specific TF genes are active in different compartments and tissues of the seed at unique times of development. Collectively, these seed-specific TF genes should facilitate the identification of regulatory networks that are important for programming seed development.

APETALA2 (AP2) plays a central role in the establishment of the floral meristem, the specification of floral organ identity, and the regulation of floral homeotic gene expression in Arabidopsis. We show here that in addition to its functions during flower development, AP2 activity is also required during seed development. We isolated the AP2 gene and found that it encodes a putative nuclear protein that is distinguished by an essential 68-amino acid repeated motif, the AP2 domain. Consistent with its genetic functions, we determined that AP2 is expressed at the RNA level in all four types of floral organs-sepals, petals, stamens, and carpels-and in developing ovules. Thus, AP2 gene transcription does not appear to be spatially restricted by the floral homeotic gene AGAMOUS as predicted by previous studies. We also found that AP2 is expressed at the RNA level in the inflorescence meristem and in nonfloral organs, including leaf and stem. Taken together, our results suggest that AP2 represents a new class of plant regulatory proteins that may play a general role in the control of Arabidopsis development.

APETALA2 (AP2) plays an important role in the control of Arabidopsis f lower and seed development and encodes a putative transcription factor that is distinguished by a novel DNA binding motif referred to as the AP2 domain. In this study we show that the AP2 domain containing or RAP2 (related to AP2) family of proteins is encoded by a minimum of 12 genes in Arabidopsis. The RAP2 genes encode two classes of proteins, AP2-like and EREBP-like, that are defined by the number of AP2 domains in each polypeptide as well as by two sequence motifs referred to as the YRG and RAYD elements that are located within each AP2 domain. RAP2 genes are differentially expressed in f lower, leaf, inf lorescence stem, and root. Moreover, the expression of at least three RAP2 genes in vegetative tissues are controlled by AP2. Thus, unlike other f loral homeotic genes, AP2 is active during both reproductive and vegetative development.Genetic and molecular studies have defined an evolutionarily conserved network of genes that control flower development in Arabidopsis and in other plant species (1, 2). In Arabidopsis, the homeotic gene APETALA2 (AP2) has been shown to control three important processes during flower development: (i) the establishment of flower meristem identity (3, 4), (ii) the specification of flower organ identity and the regulation of floral organogenesis (5-9), and (iii) the temporal and spatial regulation of flower homeotic gene activity (10). Genetic studies have shown that AP2 is also required for normal ovule and seed development (9,11,12). Consistent with its genetic functions AP2 is expressed throughout flower development, in immature floral buds, in all four types of flower organ primordia, and in developing ovules and seeds (ref. 9; B. den Boer and K.D.J., unpublished data). Unlike most other flower homeotic genes, AP2 is also expressed at the mRNA level in both stem and leaf, suggesting that AP2 may also function during vegetative development (9). However, ap2 mutant plants show no dramatic defects during either stem or leaf development. One hypothesis to explain this apparent paradox is that the Arabidopsis genome may be genetically redundant for AP2 function during stem and leaf development.Previous studies have suggested that AP2 functions as a nuclear transcription factor in plant cells (9). DNA sequence analysis showed that AP2 encodes a theoretical polypeptide of 432 amino acids that is distinct from known fungal and animal regulatory proteins (9). One important feature of the AP2 protein is a novel 68-amino acid repeated motif called the AP2 domain. The AP2 domain has been shown to be essential for AP2 functions and contains an 18-amino acid core region that is predicted to form an amphipathic ␣-helix (9). In tobacco, four AP2-like AP2 domain containing proteins have been identified (13). These proteins, referred to as the ethylene responsive element binding proteins (EREBPs), are thought to regulate gene expression at the transcriptional level. In vitro studies have shown that the EREBP AP2 do...