FLORAL SIZE MUTANT REVEAL COMPENSATION MECHANISM IN ANTIRRHINUM MAJUS

LUCIANA DELGADO-BENARROCH; BARRY CAUSIER ·; WEISS, JULIA; MARCOS EGEA-CORTINES

CARTAGENA, ESPAÑA

Congreso; X WORLD PETUNIA DAYS; 2009

Control of organ size is the product of coordinated cell division and expansion. The size of an organ depends on the number of founder cells in organ primordia, number of dividing cell and the period the cell are actively dividing followed by a period where growth occurs mainly by cell expansion. In this work we describe the Antirrhinum mutants Formosa (fo) and compacta ähnlich (coan) with specific effects over floral size. Cell size analysis of both mutants shows complex relationships between organ and cell size depending on the whorl. Both mutants have almost an opposite effect, fo increases cell number whilst coan reduce it in petals, stamen and pistil. Cell division variation appears to trigger a compensation mechanism in such a way that fo has smaller cells in petals and pistils and coan bigger cell in petals compared to wild type. In coan the increment in cell area is not related to an increment in nuclear DNA content as flow cytometry experiments show. Cell cycle activity and cell expansion were evaluated in fo through expression analysis by real-time PCR. AINTEGUMENTA (ANT) is an activator of meristematic competence in Arabidopsis and seems to have the same function in Antirrhinum. Expression analysis in inflorescence shows an up-regulation of Am-ANT in fo. Cell cycle related genes (CycD3a and Histone4) are also up-regulated in fo petals. In Arabidopsis, petal cell expansion is inhibited by the BIGPETAL (BPE) gene, and in fo mutant reduced cell size corresponded to up-regulation of an Antirrhinum BPE-like gene (Am-BPE). Our results demonstrate that floral organ size is controlled by organ specific regulation of cell division and expansion. Further more we uncovered two different compensation mechanisms in floral development, fo showed decreased cell size caused by cell number increment while coan showed the opposite effect.