Transcriptomics of Improved Fruit Retention by Hexanal in ‘Honeycrisp’ Reveals Hormonal Crosstalk and Reduced Cell Wall Degradation in the Fruit Abscission Zone

Abstract

Apples (Malus domestica Borkh) are prone to preharvest fruit drop, which is more pronounced in ‘Honeycrisp’. Hexanal is known to improve fruit retention in several economically important crops. The effects of hexanal on the fruit retention of ‘Honeycrisp’ apples were assessed using physiological, biochemical, and transcriptomic approaches. Fruit retention and fruit firmness were significantly improved by hexanal, while sugars and fresh weight did not show a significant change in response to hexanal treatment. At commercial maturity, abscisic acid and melatonin levels were significantly lower in the treated fruit abscission zone (FAZ) compared to control. At this stage, a total of 726 differentially expressed genes (DEGs) were identified between treated and control FAZ. Functional classification of the DEGs showed that hexanal downregulated ethylene biosynthesis genes, such as S-adenosylmethionine synthase (SAM2) and 1-aminocyclopropane-1-carboxylic acid oxidases (ACO3, ACO4, and ACO4-like), while it upregulated the receptor genes ETR2 and ERS1. Genes related to ABA biosynthesis (FDPS and CLE25) were also downregulated. On the contrary, key genes involved in gibberellic acid biosynthesis (GA20OX-like and KO) were upregulated. Further, hexanal downregulated the expression of genes related to cell wall degrading enzymes, such as polygalacturonase (PG1), glucanases (endo-β-1,4-glucanase), and expansins (EXPA1-like, EXPA6, EXPA8, EXPA10-like, EXPA16-like). Our findings reveal that hexanal reduced the sensitivity of FAZ cells to ethylene and ABA. Simultaneously, hexanal maintained the cell wall integrity of FAZ cells by regulating genes involved in cell wall modifications. Thus, delayed fruit abscission by hexanal is most likely achieved by minimizing ABA through an ethylene-dependent mechanism.

A Non-Shedding Fruit Elaeis oleifera Palm Reveals Perturbations to Hormone Signaling, ROS Homeostasis, and Hemicellulose Metabolism

“…Furthermore, an enrichment test found gene annotations for hormone meta olism significantly more represented in DEGs. These results suggest that the NSd fr character is caused by perturbations to the expression of genes that encode for functio involved in the transcriptional regulation and signal transduction events important f fruit shedding to take place, in particular, those related to hormones, as highlighted previous transcriptome studies [6,[33][34][35][36][37][38]. Notably, several genes with downregulat profiles encode for functions that involve plant hormone transcriptional regulation, s naling and homeostasis, including those for ethylene (ET), jasmonic acid (JA), abscisic ac (ABA), cytokinin (CK), salicylic acid (SA) and auxin (Figure 5).…”

A multifaceted comparison between the fruit-abscission and fruit-retention cultivars in ornamental crabapple

“…It is also worth noting that McTGA10 is a member of the bZIP transcription factor. TGA transcription factor can bind to downstream genes specifically to regulate fruit shedding of Phaseolus vulgaris ( Sriskantharajah et al, 2021 ). Therefore, the differential expression of McTGA10 was anticipated to mediate changes in other genes that affect the fruit abscission of ornamental crabapples.…”

Preharvest Spray Hexanal Formulation Enhances Postharvest Quality in ‘Honeycrisp’ Apples by Regulating Phospholipase D and Calcium Sensor Proteins Genes

“…We previously reported that preharvest spray hexanal formulation delayed fruit abscission in 'Honeycrisp' most likely by minimizing ABA through an ethylene-dependent mechanism [41]. Hexanal formulation also decreased storage disorder bitter pit [44].…”

“…Hexanal, a naturally occurring C6 volatile aldehyde, is a strong inhibitor of PLD activity. Hexanal also decreased ethylene in ripening fruit such as mango [39] and banana [40] and downregulated ethylene biosynthesis genes in tomato [13] and apple [41]. It has been suggested that the application of hexanal as an aqueous formulation enhanced membrane stability through inhibiting PLD activity and thereby improved marketable qualities and shelf life of several fruit and vegetables [42,43].…”