Abstract
The gynoecium is the female reproductive structure of angiosperm flowers. In Arabidopsis thaliana the gynoecium is composed of two carpels that are fused into a tube-like structure. As the gynoecial primordium arises from the floral meristem, a specialized meristematic structure, the carpel margin meristem (CMM), develops from portions of the medial gynoecial domain. The CMM is critical for reproductive competence because it gives rise to the ovules, the precursors of the seeds. Here we report a functional role for the transcription factor PERIANTHIA (PAN) in the development of the gynoecial medial domain and the formation of ovule primordia. This function of PAN is revealed in pan aintegumenta (ant) as well as seuss (seu) pan double mutants that form reduced numbers of ovules. Previously, PAN was identified as a regulator of perianth organ number and as a direct activator of AGAMOUS (AG) expression in floral whorl four. However, the seu pan double mutants display enhanced ectopic AG expression in developing sepals and the partial transformation of sepals to petals indicating a novel role for PAN in the repression of AG in floral whorl one. These results indicate that PAN functions as an activator or repressor of AG expression in a whorl-specific fashion. The seu pan double mutants also display enhanced floral indeterminacy, resulting in the formation of “fifth whorl” structures and disruption of WUSCHEL (WUS) expression patterns revealing a novel role for SEU in floral meristem termination.
Highlights
In Arabidopsis thaliana, as with most angiosperms, reproductive competence depends on the proper development of the flower
Under short-day growing conditions the severity and penetrance of seu pan gynoecial defects were enhanced relative to the long-day conditions (Figures 2G–O). (We did not examine the development of the pan ant double mutants under the short-day growing conditions.) To analyze the seu pan phenotypes under short-day conditions we scored the gynoecia for the occurrence of four phenotypes; complete loss of ovules, carpel bending, severe loss of valves, and indeterminate growth from internal gynoecial positions
AGAMOUS IS MIS-EXPRESSED IN WHORL ONE OF THE seu pan DOUBLE MUTANT FLOWERS In light of the known role of AG in regulating floral determinacy, and SEU and PAN acting as regulators of AG expression, we examined AG expression patterns in seu pan plants via in situ hybridization
Summary
In Arabidopsis thaliana, as with most angiosperms, reproductive competence depends on the proper development of the flower. Arabidopsis flowers develop from floral meristems, specialized structures that contain organized groups of undifferentiated cells that give rise to the four types of floral organs: sepals, petals, stamens, and carpels (Vaughn, 1955; Hill and Lord, 1988; Bowman et al, 1989). These four organ types develop in concentricallyorganized circular fields, termed whorls. We report that SEU plays a previously unanticipated role in floral meristem termination This is revealed by altered patterns of WUS expression and the strong enhancement of the PAN indeterminacy phenotype in the seu pan double mutants, under short-day conditions. The role of PAN and SEU during both floral meristem termination and CMM development suggest a possible link between these developmental events
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