Chapter Ten - Molecular Control of Inflorescence Development in Asteraceae

Abstract

Abstract Flowers and their arrangement in inflorescences have a key role for the reproductive success of plants as well as for crop yield. An example of the huge variation in floral and inflorescence structures is seen in the sunflower family, Asteraceae that bears complex inflorescences (capitula) that are comprised of structurally and functionally different types of flowers. In contrast to the classical models such as Arabidopsis, Antirrhinum or Petunia with single flower forms in their inflorescences, very little is known of the mechanisms regulating the capitulum organisation in Asteraceae. Molecular studies have mostly focused on Gerbera hybrida (Mutisieae), Helianthus annuus (Heliantheae) and Senecio sp. (Senecioneae) as models. Functional studies indicate that the duplicated CYCLOIDEA (CYC)/TEOSINTE BRANCHED1(TB1)-like genes encoding TCP domain transcription factors have evolved novel functions in Asteraceae to regulate flower type identity but they also perform late functions regulating flower organ growth. MADS-box genes basically follow the ‘standard’ ABCE model in regulating organ identities in Asteraceae, although the presence of an A function cannot be affirmed. Moreover, examples of sub- or neo-functionalisation of duplicated MADS-box gene family members are apparent. In summary, a few key components that regulate Asteraceae flower and inflorescence development have already been discovered. However, the detailed molecular networks involved in patterning the complex Asteraceae inflorescence, flower primordia initiation and coordination of their differential fate and growth are still largely unresolved.