The curvature of cucumber fruits is associated with spatial variation in auxin accumulation and expression of a YUCCA biosynthesis gene

Shengnan Li,Jie Luan,Zhiwei Qin,Dong Liu,Chunhong Liu,Chunhua Wang,Xiuyan Zhou,Ming Xin

doi:10.1038/s41438-020-00354-5

Abstract

Fruit curving lowers the commercial value of cucumber and leads to significant economic losses. The mechanism driving the abnormal curving of cucumber is largely unknown. Through our previous work, we discovered that 2 days post-anthesis (DPA) was the key time point at which various phenotypic and genotypic characteristics of cucumber fruits are determined. Here, we analyzed the transcriptome of the concave (C1) and convex (C2) sides of curved fruits at 2 DPA by Gene Ontology (GO) enrichment and functional pathway enrichment analyses and identified auxin as a putative factor influencing fruit curvature. Changes in the curve angle in the fruits and exogenous auxin treatment analyses showed that asymmetric auxin distribution induces fruit curving. Identification of differentially expressed genes (DEGs) related to auxin and qPCR validation showed that CsYUC10b had the most significant differential expression when both sides of the curved fruits were compared. Gene functional analysis showed that the transcript levels of CsYUC10b and the auxin concentration were even on both sides of the fruit in CsYUC10b-overexpressing plants, which in turn contributed to an equal rate of growth of both sides of cucumber fruits and resulted in a straight shape of the fruits. Thus, we conclude that CsYUC10b promotes the formation of straight cucumber fruits, with possible applications in the production and breeding of cucumber.

Highlights

Fruit shape is a critical factor determining commercial production, germplasm accession classification, and consumer preference
The C1-specific categories were enriched in protein kinase activity, the ethylene-mediated signal pathway, regulation of cell size, regulation of cell shape, and polar auxin transport (PAT)
CsYUC10b plays a crucial role in fruit curving We identified 33 auxin homeostasis-related genes from the transcriptome data of curved fruit exocarps (Table 1), of which YUC10b (Csa3G190380), Gretchen Hagen 3 (GH3).6 (Csa3G431430), auxin resistant 1 (AUX1) (Csa3G731880) and LAX2 (Csa2G264590) were differentially expressed between C1 and C2 (|log[2] ratio ≥ 1| and p value = 0.01), and only CsYUC10b and CsLAX2 were upregulated on the convex side compared to the concave side of the fruits

Summary

Introduction

Fruit shape is a critical factor determining commercial production, germplasm accession classification, and consumer preference. Cucumber (Cucumis sativus L.) is an economically important vegetable species of the family Cucurbitaceae and produces both straight and curved fruits. Fruit curving severely reduces its commercial and economic value[1]. Cucumber fruit shape is controlled by multiple genes and exhibits quantitative inheritance[2]. Different genotypic varieties of cucumber differ significantly in terms of the proportion of curved fruits versus straight fruits[3]. Little is known about the mechanisms underlying fruit curving, which is a crucial factor for developing new varieties

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