Abstract
An Arabidopsis (Arabidopsis thaliana) flower consists of four types of organs arranged in a stereotypical pattern. This complex floral structure is elaborated from a small number of floral meristem cells partitioned from the shoot apical meristem during reproductive development. The positioning of floral primordia within the periphery of the shoot apical meristem depends on transport of the phytohormone auxin with floral anlagen arising at sites of auxin maxima. An early marker of lateral organ fate is the AP2/ERF-type transcription factor AINTEGUMENTA (ANT), which has been proposed to act downstream of auxin in organogenic growth. Here, I show that the related, AINTEGUMENTA-LIKE6 (AIL6)/PLETHORA3 gene acts redundantly with ANT during flower development. ant ail6 double mutants show defects in floral organ positioning, identity, and growth. These floral defects are correlated with changes in the expression levels and patterns of two floral organ identity genes, APETALA3 and AGAMOUS. ant ail6 flowers also display altered expression of an auxin-responsive reporter, suggesting that auxin accumulation and/or responses are not normal. Furthermore, I show that ANT expression in incipient and young floral primordia depends on auxin transport within the inflorescence meristem. These results show that ANT and AIL6 are important regulators of floral growth and patterning and that they may act downstream of auxin in these processes.
Highlights
An Arabidopsis (Arabidopsis thaliana) flower consists of four types of organs arranged in a stereotypical pattern
ANT and AIL6 Regulate Flower Development ilar results were obtained by in situ hybridization examining ANT mRNA in Landsberg erecta (Ler) inflorescences treated with N-1naphthylphthalamic acid (NPA) (Fig. 9, E and F)
Auxin transport within the inflorescence meristem is necessary for high levels of ANT expression in the very earliest stages of flower development but not for ANT expression in older flowers
Summary
To investigate the function of AIL6 (At5g10510), I identified four T-DNA insertion lines (Fig. 1B; Krysan et al, 1999; Sessions et al, 2002; Alonso et al, 2003; Rosso et al, 2003). In stage 3 wild-type flowers, AG is expressed in cells of the floral meristem that will develop into the third and fourth whorls of the flower (Fig. 3H). In wild-type stage 3 flowers, LFY expression is strong and uniform throughout the sepal primordia and floral meristem (Fig. 4C). Accessory meristems in cauline leaf axils exhibit enhanced outgrowth in ant-4 ail plants (Fig. 6B) Both leaves and flowers produced by ant-4 ail plants are reduced in size compared with those from ant-4 and wild-type plants (Fig. 6, C–F). GUS activity was often highest in the central provascular tissue of developing floral organs (Fig. 8H) These differences suggest that auxin responses, distribution, and/or levels are altered in ant-4 ail flowers. ANT expression was reduced in incipient floral primordia and stage 1 and 2 flowers of NPA-treated ANT:GUS inflorescences (Fig. 9, C and D). The inability to detect changes in ANT mRNA levels in the RT-PCR experiment likely results from the very small contribution of cells from early floral primordia to the entire inflorescence harvested for the RT-PCR experiment
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