A novel role for the floral homeotic gene APETALA2 during Arabidopsis fruit development

Abstract

SUMMARYThe majority of the Arabidopsis fruit comprises an ovary with three primary tissue types: the valves, the replum and the valve margins. The valves, which are derived from the ovary walls, are separated along their entire length by the replum. The valve margin, which consists of a separation layer and a lignified layer, forms as a narrow stripe of cells at the valve-replum boundaries. The valve margin identity genes are expressed at the valve-replum boundary and are negatively regulated by FUL and RPL in the valves and replum, respectively. In ful rpl double mutants, the valve margin identity genes become ectopically expressed, and, as a result, the entire outer surface of the ovary takes on valve margin identity. We carried out a genetic screen in this sensitized genetic background and identified a suppressor mutation that restored replum development. Surprisingly, we found that the corresponding suppressor gene was AP2, a gene that is well known for its role in floral organ identity, but whose role in Arabidopsis fruit development had not been previously described. We found that AP2 acts to prevent replum overgrowth by negatively regulating BP and RPL, two genes that normally act to promote replum formation. We also determined that AP2 acts to prevent overgrowth of the valve margin by repressing valve margin identity gene expression. We have incorporated AP2 into the current genetic network controlling fruit development in Arabidopsis.

Developmental Control and Plasticity of Fruit and Seed Dimorphism in Aethionema arabicum

“…, and SHP2 (Dinneny et al, 2005;Ripoll et al, 2011). These also include genes that are known to show changes in expression pattern in other indehiscent Brassicaceae fruits (Avino et al, 2012;Mühlhausen et al, 2013).…”

The floral homeotic protein APETALA2 recognizes and acts through an AT-rich sequence element

“…This led us to question the specificity of AP2 DNA binding in vivo, especially in relation to its biological functions. AP2 has diverse biological functions such as seed development (Jofuku et al, 2005;Ohto et al, 2009), shoot apical meristem maintenance (Würschum et al, 2006), control of floral timing (Yant et al, 2010), preventing replum overgrowth during fruit development (Ripoll et al, 2011), establishment of floral meristem identity (Schultz and Haughn, 1993;Shannon and Meeks-Wagner, 1993), floral organ specification (Bowman et al, 1989;Kunst et al, 1989) and the regulation of homeotic gene expression (Drews et al, 1991). Perhaps the lack of strong inherent DNA-binding specificities underlies the diverse biological roles of AP2.…”

The Tomato FRUITFULL Homologs TDR4/FUL1 and MBP7/FUL2 Regulate Ethylene-Independent Aspects of Fruit Ripening

“…Thus, the gene regulatory networks involved in the development of both dry and fleshy fruits may be similar, although the outcomes are morphologically very different. The Arabidopsis thaliana transcription factor APETALA2 (AP2) and its tomato (Solanum lycopersicum) ortholog AP2a, for example, are both involved in fruit development, but At-AP2 regulates dehiscence zone development in the dry silique (Ripoll et al, 2011), whereas Sl-AP2a influences fleshy fruit ripening via regulation of ethylene biosynthesis and signaling (Chung et al, 2010;Karlova et al, 2011).…”