Transcriptomic signatures in seeds of apple (Malus domestica L. Borkh) during fruitlet abscission.

Sergio Ferrero,Lorenzo Carretero-Paulet,Giulia Eccher,Marta Adelina Mendes,Alessandro Botton,Simona Masiero,Lucia Colombo

doi:10.1371/journal.pone.0120503

Sergio Ferrero, Lorenzo Carretero-Paulet + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0120503

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Abstract

Abscission is the regulated process of detachment of an organ from a plant. In apple the abscission of fruits occurs during their early development to control the fruit load depending on the nutritional state of the plant. In order to control production and obtain fruits with optimal market qualities, the horticultural procedure of thinning is performed to further reduce the number of fruitlets. In this study we have conducted a transcriptomic profiling of seeds from two different types of fruitlets, according to size and position in the fruit cluster. Transcriptomic profiles of central and lateral fruit seeds were obtained by RNAseq. Comparative analysis was performed by the functional categorization of differentially expressed genes by means of Gene Ontology (GO) annotation of the apple genome. Our results revealed the overexpression of genes involved in responses to stress, hormone biosynthesis and also the response and/or transport of auxin and ethylene. A smaller set of genes, mainly related to ion transport and homeostasis, were found to be down-regulated. The transcriptome characterization described in this manuscript contributes to unravelling the molecular mechanisms and pathways involved in the physiological abscission of apple fruits and suggests a role for seeds in this process.

Highlights

IntroductionBorkh) is one of the most cultivated fruit crops around the world and is becoming a model species since the recent elucidation of its genome sequence [1]
Our seed transcriptomic data suggest that lateral fruits are ‘pre-conditioned’ to abscise, and that the effect of blooming time and fertilization as well as position inside the corymb are important for conditioning the transcriptome of the seed, leading to specific features that will decide the fate of the fruitlet according to the nutritional conditions of the plant
Seeds from lateral fruits seem to be activating a mechanism to maintain homeostasis and avoid abscission, and eventually, depending on their position in the cluster, they may be unable to avoid triggering the signal that will lead to developmental arrest and eventually abscission

Summary

Introduction

Borkh) is one of the most cultivated fruit crops around the world and is becoming a model species since the recent elucidation of its genome sequence [1]. To many other fruit crops, apple trees develop an abundance of flowers that results in an excessive fruit load with a subsequent reduction in fruit quality. Many fruit tree species have developed a system of regulation of the fruit load whereby part of it is shed during early fruit development. While in some cases abscission of fruits is sufficient for regulating the fruit load, as in some species of Citrus [2], in apple trees physiological shedding reduces the number of fruits insufficiently [3,4,5].

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