Stem Cell Signaling During Capitulum Development

Capitulum-type inflorescences are found throughout the sunflower family and are thought to have evolved following the compaction (height) and expansion (width) of a more diffuse flowering shoot. After transition to flowering, most plants will initiate flower development immediately and maintain continuous flower production during inflorescence formation (typical of diverse inflorescence-types such as racemes, thyrses, spikes, etc.). In contrast, capitulum development has a period of prolonged "quiescence" in the inflorescence meristem, when there is little organ proliferation, facilitating the lateral expansion of this tissue prior to flower initiation (Figure 1). The Jones lab is interested in identifying signaling mechanisms that directly contribute to capitulum expansion and developmental timing of floret initiation, centered around understanding the role of conserved stem cell signaling pathways (such as CLAVATA signaling) in regulating meristem expansion.

 Figure 1 – Capitulum formation in sunflower with key developmental stages. Stages: vegetative meristem phase (VM), transitional meristem phase (TM), inflorescence meristem expansion phase (Exp), and floral meristem differentiation phase (FM). CLAVATA3 (CLV3, peptide hormone that regulates stem cell identity) expression shown in pink (low) and red (high) from in situ and RNAseq analysis. 

Floral development

Young sunflower capitulum with developing flowers inside the bud (confocal microscopy)

Variation in Sunflower

"Core 12" set of sunflower accessions (SAM population - Mandel et al., Theor Appl Genet, 2011)

Wild and cultivated sunflowers display an enormous amount of phenotypic variation, especially in traits like capitulum size. We are using developmental transcriptomics and natural genetic variation across sunflower accessions to identify genes regulating meristem expansion and maturation during capitulum formation.

Bidens cv. Compact Yellow at UNC Spring 2021

Developmental Model

While many genetic models are currently utilized in the Asteraceae (such as Gerbera, lettuce, sunflower), no broadly adopted developmental model system has been established. This is likely due to many key limitations of current models, including: genome size, genomic heterozygosity, plant size/stature, and ease of transformation. Our lab is looking to develop a new model species in the Asteraceae to facilitate the identification of novel genes regulating capitulum development. This new model system will be small in size, a rapid life cycle, a small diploid genome, and have efficient transformation capabilities.

Platycodon grandiflorus (Campanulaceae) 

Asterales genomics

The Asterales are an order of flowering plants that contain between ~10-12% of all flowering plant species, with the sunflower family representing the bulk of these taxa. While vast in number, relatively few genomic resources exist across many of these groups restricting comparative analyses. Through a collaborative effort with several groups, we are building chromosome-scale reference quality genomes across multiple families in the Asterales using a combination of long-read DNA and HiC sequencing/analysis.