Gibberellins are required for dimorphic flower development in Viola philippica

Area of Science:

• Plant Biology
• Developmental Biology
• Genetics

Background:

• Photoperiod is a key environmental cue influencing plant development, including flower morphology.
• Viola philippica exhibits dimorphic flower development, producing chasmogamous (CH) and cleistogamous (CL) flowers under different photoperiodic conditions.
• Cleistogamous (CL) flowers are induced exclusively under long-day (LD) conditions, while chasmogamous (CH) flowers develop under short-day (SD) conditions.

Purpose of the Study:

• To investigate the role of gibberellin (GA) in mediating photoperiod-induced dimorphic flower development in Viola philippica.
• To characterize the expression patterns of key GA synthesis genes, VpGA20ox and VpGA3ox, in relation to floral organ development.
• To elucidate the molecular mechanisms by which GA signaling interacts with MADS-box genes to regulate floral dimorphism.

Main Methods:

• Quantification of active gibberellin (GA) content in floral buds under different photoperiods.
• Molecular characterization and expression analysis of V. philippica GA 20-oxidase (VpGA20ox) and GA 3-oxidase (VpGA3ox) genes.
• Application of paclobutrazol (GA synthesis inhibitor) and exogenous GAs to assess their effects on floral development and gene expression.
• Analysis of B-class MADS-box gene expression in relation to GA treatment and photoperiod.

Main Results:

• Active GA content was higher in CL floral buds under LD conditions, suggesting GA biosynthesis is enhanced by longer photoperiods.
• VpGA20ox and VpGA3ox expression correlated with GA accumulation in floral organs; GAs accumulated in stamens and petals under SD, promoting their development, while low GA content under LD led to poor development.
• Exogenous GA application partially induced the transition from CH to CL flowers under SD, accompanied by downregulation of B-class MADS-box genes, which also showed similar expression profiles to VpGA20ox and VpGA3ox in stamen and petal development.
• GA signaling appears to regulate dimorphic flower development by affecting B-class homeotic gene expression in response to photoperiod.

Conclusions:

• Gibberellin (GA) signaling plays a crucial role in photoperiod-dependent regulation of dimorphic flower development in Viola philippica.
• GA signaling interacts with B-class MADS-box genes to control the development of floral organs, leading to CH and CL flower formation.
• The study provides insights into the molecular basis of floral dimorphism and its evolutionary significance in Viola.