\u3cem\u3eAINTEGUMENTA\u3c/em\u3e Contributes to Organ Polarity and Regulates Growth of Lateral Organs in Combination with \u3cem\u3eYABBY\u3c/em\u3e Genes

Lateral organs in flowering plants display polarity along their adaxial-abaxial axis with distinct cell types forming at different positions along this axis. Members of three classes of transcription factors in Arabidopsis (Arabidopsis thaliana; the Class III homeodomain/leucine zipper [HD-ZIP] proteins, KANADI proteins, and YABBY proteins) are expressed in either the adaxial or abaxial domain of organ primordia where they confer these respective identities. Little is known about the factors that act upstream of these polarity-determining genes to regulate their expression. We have investigated the relationship between AINTEGUMENTA (ANT), a gene that promotes initiation and growth of lateral organ primordia, and polarity genes. Although ant single mutants do not display any obvious defects in organ polarity, loss of ANT activity in combination with mutations in one or more YABBY genes results in polarity defects greater than those observed in the yabby mutants alone. Our results suggest that ANT acts in combination with the YABBY gene FILAMENTOUS FLOWER (FIL) to promote organ polarity by upregulating the expression of the adaxial-specifying HD-ZIP gene PHABULOSA. Furthermore, we show that ANT acts with FIL to up-regulate expression of the floral homeotic gene APETALA3. Our work defines new roles for ANT in the development of lateral organs

Synergistic disruptions in seuss cyp85A2 double mutants reveal a role for brassinolide synthesis during gynoecium and ovule development

<p>Abstract</p> <p>Background</p> <p>The Arabidopsis <it>SEUSS </it>(<it>SEU</it>) gene encodes a transcriptional adaptor protein that is required for a diverse set of developmental events, including floral organ identity specification, as well as gynoecium, ovule and embryo development. In order to better understand the molecular mechanisms of <it>SEUSS </it>action we undertook a genetic modifier screen to identify <it>seuss-modifier </it>(<it>sum</it>) mutations.</p> <p>Results</p> <p>Screening of M2 lines representing approximately 5,000 M1 individuals identified mutations that enhance the <it>seuss </it>mutant phenotypic disruptions in ovules and gynoecia; here we describe the phenotype of the <it>sum63 </it>mutant and enhanced disruptions of ovule and gynoecial development in the <it>seu sum63 </it>double mutant. Mapping and genetic complementation tests indicate that <it>sum63 </it>is allelic to <it>CYP85A2 </it>(AT3G30180) a cytochrome p450 enzyme that catalyzes the final steps in the synthesis of the phytohormone brassinolide.</p> <p>Conclusions</p> <p>Our identification of mutations in <it>CYP85A2 </it>as enhancers of the <it>seuss </it>mutant phenotype suggests a previously unrecognized role for brassinolide synthesis in gynoecial and ovule outer integument development. The work also suggests that <it>seuss </it>mutants may be more sensitive to the loss or reduction of brassinolide synthesis than are wild type plants.</p

DNA Binding Properties of the \u3cem\u3eArabidopsis\u3c/em\u3e Floral Development Protein AINTEGUMENTA

The Arabidopsis protein AINTEGUMENTA (ANT) is a member of a plant-specific family of transcription factors (AP2/EREBP) that share either one or two copies of an approximately 70 amino acid region called the AP2 repeat. DNA binding activity has been demonstrated previously for members of this family containing a single AP2 repeat. Using an in vitro selection procedure, the DNA binding specificity of the two AP2 repeat containing protein ANT was found to be 5\u27-gCAC(A/G)N(A/T)TcCC(a/g)ANG(c/t)-3\u27. This consensus site is much longer than sites recognized by proteins containing a single AP2 repeat and neither AP2 repeat of ANT was alone capable of binding to the selected sequences, suggesting that both AP2 repeats make DNA contacts. ANT binds to these DNA sequences as a monomer but a higher order complex is also observed at high protein concentrations. The ANT consensus site shows some similarity to the C-repeat/DRE elements bound by proteins that contain a single AP2 repeat, and we find that ANT binds weakly to such sites. We propose a model in which each AP2 repeat of ANT contacts adjacent sites within the consensus sequence. Our results suggest that the AP2 repeat can be utilized in different ways for DNA binding

DNA binding properties of the Arabidopsis floral development protein AINTEGUMENTA

The Arabidopsis protein AINTEGUMENTA (ANT) is a member of a plant-specific family of transcription factors (AP2/EREBP) that share either one or two copies of an approximately 70 amino acid region called the AP2 repeat. DNA binding activity has been demonstrated previously for members of this family containing a single AP2 repeat. Using an in vitro selection procedure, the DNA binding specificity of the two AP2 repeat containing protein ANT was found to be 5′-gCAC(A/G)N(A/T)TcCC(a/g)ANG(c/t)-3′. This consensus site is much longer than sites recognized by proteins containing a single AP2 repeat and neither AP2 repeat of ANT was alone capable of binding to the selected sequences, suggesting that both AP2 repeats make DNA contacts. ANT binds to these DNA sequences as a monomer but a higher order complex is also observed at high protein concentrations. The  ANT consensus site shows some similarity to the C-repeat/DRE elements bound by proteins that contain a single AP2 repeat, and we find that ANT binds weakly to such sites. We propose a model in which each AP2 repeat of ANT contacts adjacent sites within the consensus sequence. Our results suggest that the AP2 repeat can be utilized in different ways for DNA binding

AINTEGUMENTA Contributes to Organ Polarity and Regulates Growth of Lateral Organs in Combination with YABBY Genes

Lateral organs in flowering plants display polarity along their adaxial-abaxial axis with distinct cell types forming at different positions along this axis. Members of three classes of transcription factors in Arabidopsis (Arabidopsis thaliana; the Class III homeodomain/leucine zipper [HD-ZIP] proteins, KANADI proteins, and YABBY proteins) are expressed in either the adaxial or abaxial domain of organ primordia where they confer these respective identities. Little is known about the factors that act upstream of these polarity-determining genes to regulate their expression. We have investigated the relationship between AINTEGUMENTA (ANT), a gene that promotes initiation and growth of lateral organ primordia, and polarity genes. Although ant single mutants do not display any obvious defects in organ polarity, loss of ANT activity in combination with mutations in one or more YABBY genes results in polarity defects greater than those observed in the yabby mutants alone. Our results suggest that ANT acts in combination with the YABBY gene FILAMENTOUS FLOWER (FIL) to promote organ polarity by up-regulating the expression of the adaxial-specifying HD-ZIP gene PHABULOSA. Furthermore, we show that ANT acts with FIL to up-regulate expression of the floral homeotic gene APETALA3. Our work defines new roles for ANT in the development of lateral organs

A Molecular Framework for Auxin-Mediated Initiation of Flower Primordia

SummaryA classical role of the hormone auxin is in the formation of flowers at the periphery of the reproductive shoot apex. Mutants in regulators of polar auxin transport or in the auxin-responsive transcription factor MONOPTEROS (MP) form naked inflorescence “pins” lacking flowers. How auxin maxima and MP direct initiation of flower primordia is poorly understood. Here, we identify three genes whose expression is directly induced by auxin-activated MP that furthermore jointly regulate flower primordium initiation. These three genes encode known regulators of flower development: LEAFY (LFY), which specifies floral fate, and two AINTEGUMENTA-LIKE/PLETHORA transcription factors, key regulators of floral growth. Our study thus reveals a mechanistic link between flower primordium initiation and subsequent steps in flower morphogenesis. Finally, we uncover direct positive feedback from LFY to the auxin pathway. The auxin LFY module we describe may have been recruited during evolution to pattern other plant organ systems