Early thinning of peach fruit influences expression of cell growth and expansion genes

Abstract

The effects of crop reduction during early development of peach fruits on gene expression were investigated. Flowers or fruitlets of four different cultivars of Prunus persica, ‘Carored’, ‘Summerprince’, ‘Redhaven’ and ‘Scarletprince’, were thinned one week (early thinning) and/or four weeks (late thinning) after full bloom in two consecutive years (2014-2015). In 2014, early thinning of all cultivars correlated with increased mesocarp cell number, cell size, and fruit size compared to their respective late-thinned trees. Expression levels of five growth-regulatory genes, FW2.2, CNR12, TAGL1, SIM, and ANT in fruit and leaf tissue were evaluated using qPCR. FW2.2 expression was 12.8 and 4.5-fold higher in early-thinned ‘Carored’ and ‘Scarletprince’, respectively, compared to late-thinned trees. Bloom-thinned ‘Carored’ showed negligible differential expression of CNR12, TAGL1, ANT, and SIM compared to the late-thinned group. The early-thinned fruitlets of ‘Scarletprince’ showed reduced expression of all analyzed genes compared to the late-thinned trees. RNA-Seq analysis revealed significant up and down-regulation for a large number of genes involved in lipid metabolism, translation, redox reactions, and other processes important for cell growth and division. RNA-Seq also revealed a much higher change in gene expression in samples taken earlier during fruit development, suggesting that early responses to thinning are what lead to increased fruit size. Ongoing research will continue to investigate which cellular processes are regulated in response to reduced crop load and how this leads to larger fruit size.