Differential behavior within a grapevine cluster: decreased ethylene-related gene expression dependent on auxin transport is correlated with low abscission of first developed berries.

Nathalie Kühn,Carlos Abello,Serge Delrot,Patricio Arce-Johnson,Francisca Godoy

doi:10.1371/journal.pone.0111258

Abstract

In grapevine, fruit abscission is known to occur within the first two to three weeks after flowering, but the reason why some berries in a cluster persist and others abscise is not yet understood. Ethylene sensitivity modulates abscission in several fruit species, based on a mechanism where continuous polar auxin transport across the pedicel results in a decrease in ethylene perception, which prevents abscission. In grapevine, flowering takes about four to seven days in a single cluster, thus while some flowers are developing into berries, others are just starting to open. So, in this work it was assessed whether uneven flowering accounted for differences in berry abscission dependent on polar auxin transport and ethylene-related gene expression. For this, flowers that opened in a cluster were tagged daily, which allowed to separately analyze berries, regarding their ability to persist. It was found that berries derived from flowers that opened the day that flowering started – named as “first berries” – had lower abscission rate than berries derived from flowers that opened during the following days – named as “late berries”. Use of radiolabeled auxin showed that “first berries” had higher polar auxin transport, correlated with lower ethylene content and lower ethylene-related transcript abundance than “late berries”. When “first berries” were treated with a polar auxin transport inhibitor they showed higher ethylene-related transcript abundance and were more prone to abscise than control berries. This study provides new insights on fruit abscission control. Our results indicate that polar auxin transport sustains the ability of “first berries” to persist in the cluster during grapevine abscission and also suggest that this could be associated with changes in ethylene-related gene expression.

Highlights

Survival within a community depends on several genetic and environmental factors that define which organisms will be able to maintain their reproductive cycle, while others stop their development
As polar auxin transport has been connected to abscission, we investigated whether variations in abscission rate correlated with differences in polar auxin transport capacity
Polar auxin transport impairment caused by N-1naphthylphthalamic acid (NPA) treatment, resulted in a slight but significant increase in abscission percentage, indicating that polar auxin transport across the berry is required to reduce abscission. These results suggest that the ability of ‘‘first berries’’ to persist in a cluster is based on the capacity to sustain polar transport of auxin, which is associated with changes in the expression of genes involved in ethylene biosynthesis and perception

Summary

Introduction

Survival within a community depends on several genetic and environmental factors that define which organisms will be able to maintain their reproductive cycle, while others stop their development. This notion may be applied to determined cells or tissues that are predestined to survive. What does determine this successful status, is an interesting question not always easy to solve. Many fruit species that produce abundant flowers are not able to support the growth of all fruits, and some of them are selected to continue their growth, with fruit abscission the selection mechanism involved. Fruit abscission, described as the physiological drop of fruitlets, allows to define how many fruits will persist, ensuring an adequate destination of photosynthates, water and ions. Plants bearing a heavy fruit load per cluster show higher fruit abscission rates compared to plants with a small number of fruits [1], indicating that there is a control of the fruit load and that abscission has a key role

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