Comparative transcriptomic analysis of apple and peach fruits: insights into fruit type specification.

Authors: LI, MUZI - University Of Maryland; Galimba, Kelsey; XIAO, YUWEI - University Of Maryland; Dardick, Christopher - Chris; MOUNT, STEPHEN - University Of Maryland; Callahan, Ann; LIU, ZONGCHI - University Of Maryland

Submitted to: The Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/2021
Publication Date: 12/14/2021
Citation: Li, M., Galimba, K.D., Xiao, Y., Dardick, C.D., Mount, S., Callahan, A.M., Liu, Z. 2021. Comparative transcriptomic analysis of apple and peach fruits: insights into fruit type specification. The Plant Journal. 109:1614-1629. https://doi.org/10.1111/tpj.15633.
DOI: https://doi.org/10.1111/tpj.15633

Interpretive Summary: This study examined gene expression patterns in fruit tissue that becomes the edible/fleshy part of the fruit. Peaches and apples were used because for peaches the ovary wall of the fruit becomes the juicy flesh while in apple the base of the flower becomes the fleshy juicy part while the ovary wall forms the core. Both fruit species are in the Rose family and have closely related genes but apple has a duplicated genome. Many of the gene expression patterns were very similar but several regulatory genes appeared to be correlated with which tissue becomes fleshy. Some of these genes decrease in expression before the tissue becomes fleshy and the others increase in expression before the tissue becomes fleshy. A model of gene action is presented that extends the idea of which genes regulate flower and fruit development to include genes that determine whether or not the fruit tissue is fleshy. These genes will be tested in the future. One of the benefits of studies like this is the potential to form fleshy fruit even without pollination or following frost damage.

Technical Abstract: Utilizing comparative transcriptomic analyses, the molecular mechanisms underlying fleshy fruit diversity was examined. The Rosaceae family represents diverse fruit forms ranging from dry to fleshy of which apple (Malus domestica) and peach (Prunus persica) have fleshy fruit but in apple, a pome, it is derived from the hypanthium tissue and in peach, a drupe, it is from the ovary wall and is a true botanical fruit. RNAseq was performed on hypanthium, ovary wall and seed/ovule tissues from apple and peach at early fruit stages, (0-20 days after full bloom) which encompassed pre-pollination, pollination and post-fertilization stages of fruit development. MADS box genes PI and TM6 were identified as potential negative regulators of flesh development and FBP9, FUL and API/CALI as positive regulators of flesh development in both apple and peach. Increases in photosynthesis gene expression also appeared to be correlated with flesh development. A comparison of the presence and duplication of these genes in eudicots was examined to look for associations with the fleshy fruit type. A modification of the ABCD flower regulation model is proposed to account for fleshy fruit development regulation.