HD-ZIP Transcription Factors and Brassinosteroid Signaling Play a Role in Capitulum Patterning in Chrysanthemum

• Published in: International journal of molecular sciences Vol. 24; no. 8; p. 7655
• Main Authors: Castricum, Annemarie, Bakker, Erin H, de Vetten, Nick C M H, Weemen, Mieke, Angenent, Gerco C, Immink, Richard G H, Bemer, Marian
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 21.04.2023; MDPI
• Subjects: Analysis; Brassinosteroids; capitulum; Chrysanthemum; Chrysanthemum - genetics; Chrysanthemum - metabolism; disc floret; DNA binding proteins; Flowers - genetics; Flowers - metabolism; Gene Expression Regulation, Plant; HD-ZIP IV; High-definition television; Plant Breeding; ray floret; Transcription Factors - genetics; Transcription Factors - metabolism; Netherlands; disc floret; HD-ZIP IV; ray floret; Chrysanthemum; brassinosteroids; capitulum
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms24087655

Chrysanthemum is a genus in the Asteraceae family containing numerous cut flower varieties with high ornamental value. It owes its beauty to the composite flower head, which resembles a compact inflorescence. This structure is also known as a capitulum, in which many ray and disc florets are densely packed. The ray florets are localized at the rim, are male sterile, and have large colorful petals. The centrally localized disc florets develop only a small petal tube but produce fertile stamens and a functional pistil. Nowadays, varieties with more ray florets are bred because of their high ornamental value, but, unfortunately, this is at the expense of their seed setting. In this study, we confirmed that the disc:ray floret ratio is highly correlated to seed set efficiency, and therefore, we further investigated the mechanisms that underlie the regulation of the disc:ray floret ratio. To this end, a comprehensive transcriptomics analysis was performed in two acquired mutants with a higher disc:ray floret ratio. Among the differentially regulated genes, various potential brassinosteroid (BR) signaling genes and HD-ZIP class IV homeodomain transcription factors stood out. Detailed follow-up functional studies confirmed that reduced BR levels and downregulation of HD-ZIP IV gene ( ) result in an increased disc:ray floret ratio, thereby providing ways to improve seed set in decorative chrysanthemum varieties in the future.