Ethylene-regulated immature fruit abscission is associated with higher expression of CoACO genes in Camellia oleifera.

Xiao Hu,Shoufu Gong,Muhammad Sajjad,Xiaoling Ma,Deyi Yuan,Hongbo Li,Jian Zhang,Mi Yang

doi:10.1098/rsos.202340

Abstract

Immature fruit abscission is a key limiting factor in Camellia oleifera Abel. (C. oleifera) yield. Ethylene is considered to be an important phytohormone in regulating fruit abscission. However, the molecular mechanism of ethylene in regulating fruit abscission in C. oleifera has not yet been studied. Here, we found that the 1-aminocyclopropane-1-carboxylic acid (ACC) content was significantly increased in the abscission zones (AZs) of abnormal fruits (AF) which were about to abscise when compared with normal fruits (NF) in C. oleifera ‘Huashuo’. Furthermore, exogenous ethephon treatment stimulated fruit abscission. The cumulative rates of fruit abscission in ethephon-treated fruits (ETH-F) on the 4th (35.0%), 8th (48.7%) and 16th (57.7%) days after treatment (DAT) were significantly higher than the control. The ACC content and 1-aminocyclopropane-1-carboxylate oxidase (ACO) activity in AZs of ETH-F were also significantly increased when compared with NF on the 4th and 8th DAT. CoACO1 and CoACO2 were isolated in C. oleifera for the first time. The expressions of CoACO1 and CoACO2 were considerably upregulated in AZs of AF and ETH-F. This study suggested that ethylene played an important role in immature fruit abscission of C. oleifera and the two CoACOs were the critical genes involved in ethylene's regulatory role.

Highlights

Camellia oleifera Abel. (C. oleifera) is widely cultivated in southern China
The expression level of CoACO2 in abscission zones (AZs) of ethephon-treated fruits (ETH-F) was significantly increased to about 188.1-fold, 30.7-fold and 21.4-fold higher than that in control on the 4th, 8th and 16th days after treatment (DAT), respectively. These results indicate that CoACO1 and CoACO2 genes have an association with fruit abscission at the August stage in C. oleifera
The ACC content and ACC oxidase (ACO) activity were higher in AZs of abnormal fruits (AF) than in that of normal fruits (NF)

Summary

Introduction

Camellia oleifera Abel. (C. oleifera) is widely cultivated in southern China. It is one of the top four (oil palm, olive, coconut, camellia) globally grown woody oil plants [1]. In China, the cultivation area of C. oleifera is expanding with fruit abscission as the major yield-limiting factor. The flower and fruit abscission rates are very high, ranging between 10–25% and 15– 20%, respectively, which seriously affect the yield in C. oleifera. Applied ethephon stimulates ethylene production and triggers ethylene-dependent reactions such as flower or fruit abscission [12]. It has been shown that ethylene is the main signal molecule to induce fruit abscission in apple, oil palm and litchi [13,14,15]. Ethylene biosynthesis may be involved in the abscission process, and it plays an important role in the final stage of abscission. The importance of ACO in regulating the production of ethylene in plants has been proved gradually. ACO plays an important role in the post-climacteric ripening of tomato fruits. Many ACO genes were identified in apple (7), Arabidopsis (5), tomato (7), rice (9) and maize (13) [19]

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