Gillenia trifoliata: a tool to understand the genetic regulation of apple flesh development

Fleshy fruits have evolved independently multiple times from dry fruit ancestors, suggesting fruit fleshiness evolves with relative ease (Bremer & Eriksson, 1992; Clausing & Renner, 2001; S. Knapp, 2002; Potter et al., 2007). Apple flesh putatively evolved via progressive floral fusions and acquisition of competency of floral tissues to become fleshy (Rohrer et al., 1994; Evans & Dickinson, 2005; Potter, et al., 2007; Xiang et al., 2017; Z. Liu et al., 2020). Gillenia is sister taxon to the Maleae (apple) tribe and data supports an autopolyploidisation origin for the Maleae tribe from the ancestral lineage which includes extant Gillenia (Evans & Campbell, 2002; Velasco et al., 2010). Gillenia bears the putative ancestral dry fruit type of the subfamily to which it belongs, which lacks both floral fusions and flesh competency. In apple, the homoeologous MADS-box genes, SEPALLATA1/2-like MdMADS8/9, appear to regulate flesh competency, because suppression of both genes (MADS8as) produces fleshless apples (Ireland et al., 2013) and MdMADS8 over-expression produced apples with more flesh (Hoong et al., under revision). The aim of this thesis was to understand the genetic regulation of apple flesh development using Gillenia as a negative control. Firstly, phenological and genomic resources were established for Gillenia (Ireland, Wu, et al., 2021), and together provide an interspecies standardisation tool and genomic resource for comparative analyses. Genome-wide analysis of select gene families revealed conserved genome dynamics related to flower and fruit development. Interspecies comparative transcriptomics and bioinformatics revealed the importance of A- and E-type MADS-box genes for apple fruit development and identified a co-expression module involving MdMADS8 with potential to be a master switch for flesh development. Using Gillenia and MADS8as as negative controls, comparative transcriptomics, microstructural anatomy and MdMADS8 immunolocalisation, revealed post-pollination regulation of flesh development by MdMADS8. Processes related to hormones, cell cycle, cell expansion, and cell wall modification, with associated putative direct targets were identified and a model is presented suggesting MdMADS8 regulates flesh development by promoting processes that enhance flesh and suppressing processes that hinder flesh. Lastly, insights into pome evolution were gained, such as the identification of a conserved loss of a BELLRINGER-related gene in Maleae, and a role for MdMADS8 in regulating carpel fusion.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Biological Sciences

Grantor dc:publisher

ResearchSpace@Auckland

Year dc:date.issued

2023

Author dc:creator

• Ireland, Hilary Sara

Advisors dc:contributor.advisor

• Schaffer, Robert
• David, Karine

Statement dc:rights

• Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

Licence dc:rights.uri

• https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm

Handle dc:identifier.uri

https://hdl.handle.net/2292/65108

OAI identifier oai:identifier

oai:researchspace.auckland.ac.nz:2292/65108