Gibberellic acid induced parthenocarpic 'Honeycrisp' apples (Malus domestica) exhibit reduced ovary width and lower acidity. Issue 1 (6th April 2019)

• Record Type: Journal Article
• Authors: Galimba, Kelsey D; Bullock, Daniel G; Dardick, Chris; Liu, Zhongchi; Callahan, Ann M
• Is Part Of: Horticulture research. Volume 6:Issue 1(2019)
• Publication Date: 2019-04-06
• Subjects: Agricultural genetics -- Fruiting -- Gibberellins -- Plant molecular biology; Horticulture -- Research -- Periodicals; 635.072
• DOI: 10.1038/s41438-019-0124-8
• Languages: English
• ISSNs: 2052-7276

Abstract

Abstract: Fruit set and development are dependent on auxin, gibberellin, and cytokinin, which cause parthenocarpic development in many species when applied ectopically. Commercial sprays containing these hormones are used to improve apple fruit set, size, and shape, but have been implicated negatively in other aspects of fruit quality. We applied gibberellic acid (GA3 ), synthetic auxin (NAA), and the auxin-transport inhibitor NPA to 'Honeycrisp' apple flowers. Fruit retention and size were quantified throughout development, and seed number and fruit quality parameters were measured at maturity. GA3 alone caused the development of seedless parthenocarpic apples. At maturity, GA3 -treated apples were narrower due to reduced ovary width, indicating that GA3 induced normal growth of the hypanthium, but not the ovary. GA3 -treated fruits were also less acidic than hand-pollinated controls, but had similar firmness, starch, and sugar content. To further understand the regulation of parthenocarpy, we performed tissue-specific transcriptome analysis on GA3 -treated, NAA-treated, and control fruits, at 18 days after treatment and again at maturity. Overall, transcriptome analysis showed GA3 -treated and hand-pollinated fruits were highly similar in RNA expression profiles. Early expression differences in putative cell division, cytokinin degradation, and cell wall modification genes in GA3 -treated ovaries correlated with the observed shape differences, while early expression differences in the acidity gene Ma1 may be responsible for the changes in pH. Taken together, our results indicate that GA3 triggers the development of parthenocarpic apple fruit with morphological deviations that correlate with a number of candidate gene expression differences. Apples: Seedless 'Honeycrisp' fruit develop small cores with less acidity: Apple trees sprayed with a plant growth hormone called gibberellic acid develop seedless fruit that show morphological differences explained by changes in gene expression profiles. Ann Callahan from the US Department of Agriculture in Kearneysville, West Virginia, and colleagues showed that gibberellic acid induces flowers of the 'Honeycrisp' apple variety to develop fruit without fertilization, a process known as parthenocarpy. These fruit were seedless, with a thinner ovary at the fruit's core and a lower acid content compared to normally pollinated controls. The researchers analyzed gene activity patterns 18 days after hormone treatment. They found differences in the expression levels of genes involved in cell division, hormone metabolism and cell wall dynamics, plus lower levels of an acidity-associated gene during early ovary development. The findings show that parthenocarpic Honeycrisp apples are possible, although they exhibit quality differences.