The ambiguous ripening nature of the fig (Ficus carica L.) fruit: a gene-expression study of potential ripening regulators and ethylene-related genes.

Zohar E Freiman,Yogev Rosianskey,Moshe A Flaishman,Itzhak Kamara,Rajeswari Dasmohapatra

doi:10.1093/jxb/erv140

Zohar E Freiman, Yogev Rosianskey + Show 3 more

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https://doi.org/10.1093/jxb/erv140

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Abstract

The traditional definition of climacteric and non-climacteric fruits has been put into question. A significant example of this paradox is the climacteric fig fruit. Surprisingly, ripening-related ethylene production increases following pre- or postharvest 1-methylcyclopropene (1-MCP) application in an unexpected auto-inhibitory manner. In this study, ethylene production and the expression of potential ripening-regulator, ethylene-synthesis, and signal-transduction genes are characterized in figs ripening on the tree and following preharvest 1-MCP application. Fig ripening-related gene expression was similar to that in tomato and apple during ripening on the tree, but only in the fig inflorescence-drupelet section. Because the pattern in the receptacle is different for most of the genes, the fig drupelets developed inside the syconium are proposed to function as parthenocarpic true fruit, regulating ripening processes for the whole accessory fruit. Transcription of a potential ripening regulator, FcMADS8, increased during ripening on the tree and was inhibited following 1-MCP treatment. Expression patterns of the ethylene-synthesis genes FcACS2, FcACS4, and FcACO3 could be related to the auto-inhibition reaction of ethylene production in 1-MCP-treated fruit. Along with FcMADS8 suppression, gene expression analysis revealed upregulation of FcEBF1, and downregulation of FcEIL3 and several FcERFs by 1-MCP treatment. This corresponded with the high storability of the treated fruit. One FcERF was overexpressed in the 1-MCP-treated fruit, and did not share the increasing pattern of most FcERFs in the tree-ripened fig. This demonstrates the potential of this downstream ethylene-signal-transduction component as an ethylene-synthesis regulator, responsible for the non-climacteric auto-inhibition of ethylene production in fig.

Highlights

In the last few years, fruit-ripening research has challenged the classical definitions of climacteric and non-climacteric fleshy fruits (Paul et al, 2012)
Samples subjected to ethylene-production measurements and gene-expression quantification were as follows: ripening-onset fruit before treatment; fruit after overnight 1-MCP treatment/untreated tagged control; commercially mature fruit harvested 3 days after treatment/control; treated/control fruit subjected to storage; treated/control fruit subjected to shelf simulation (Fig. 1B)
The second system examined was preharvest 1-MCPtreated fruit stored under commercial conditions (1–2°C) and subjected to shelf simulation (20°C) (Fig. 1B)

Summary

Introduction

In the last few years, fruit-ripening research has challenged the classical definitions of climacteric and non-climacteric fleshy fruits (Paul et al, 2012). The ripening process in fig fruit is categorized as climacteric, showing a rise in respiration rate and ethylene production at the onset of the ripening phase (Marei and Crane, 1971). In addition to the auto-inhibitory reaction of ethylene production in the climacteric-classified fig, other unique characteristics of this fruit differentiate it from the well-studied Solanum lycopersicum (tomato) climacteric model. (banana) fruits, for example, reach their final size at the mature green stage, and only are the ripening processes initiated. Tomato fruit can be picked at the mature green stage and still develop to the red ripe stage within 10 days, whereas ripening of non-harvested tomato can take over 20 days (Yokotani et al, 2009; Van de Poel et al, 2013)

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