Melatonin Induces Parthenocarpy by Regulating Genes in Gibberellin Pathways of 'Starkrimson' Pear (Pyrus communis L.).

Jianlong Liu,Zhigang Wang,Fengxia Liu,Lulu Liu,Yingxiao Zhao,Fengwang Ma,Lingfei Xu,Rui Zhai,Huibin Wang,Chengquan Yang

doi:10.3389/fpls.2018.00946

Jianlong Liu, Zhigang Wang + Show 8 more

Open Access

https://doi.org/10.3389/fpls.2018.00946

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Abstract

Parthenocarpy, the production of seedless fruit without fertilization, has a variety of valuable qualities, especially for self-incompatible species, such as pear. To explore whether melatonin (MT) induces parthenocarpy, we used ‘Starkrimson’ pear as a material for morphological observations. According to our results, exogenous MT promoted the expansion and division of the mesocarp cells in a manner similar to hand pollination. However, the seeds of exogenous MT-treated fruit were undeveloped and aborted later in the fruit-setting stage. To further investigate how MT induced parthenocarpy, we studied changes of related hormones in the ovaries and found that MT significantly increased the contents of the gibberellins (GAs) GA3 and GA4. Thus, paclobutrazol (PAC), a GA-biosynthesis inhibitor, was used to study the relationship between GAs and MT. In addition, spraying MT after treatment with PAC did not increase GA content nor lead to parthenocarpy. Through a transcriptome analysis, we discovered that MT can cause significant upregulation of PbGA20ox and downregulation of PbGA2ox. However, no significant difference was observed in PbGA2ox compared with the control after PAC and MT applications. Thus, MT induces parthenocarpy by promoting GA biosynthesis along with cell division and mesocarp expansion in pear.

Highlights

Parthenocarpy, the production of seedless fruit, induces fruit development naturally or artificially without the fertilization of ovules (Gustafson, 1942)
To investigate the effects of MT on fruit set, pear plant at the full-bloom stage were subjected to four treatments
Nonpollination-treated and IAA-treated ovaries did not develop normally, but the MT-treated ovaries were similar in size to those that were hand pollinated at 10 days after anthesis (DAA) (Figure 1)

Summary

Introduction

Parthenocarpy, the production of seedless fruit, induces fruit development naturally or artificially without the fertilization of ovules (Gustafson, 1942). As an important cultivated fruit worldwide, most pears are self-unfruitful because of their gametophytic self-incompatibility. Determining an efficient method to produce pear fruit by parthenocarpy is important. Plant hormones affect fruit set, growth and development (Srivastava and Handa, 2005). Parthenocarpy can be induced by exogenous applications of plant hormones. Most genes involved in fruit set are related to growth regulators of fruit development, such as gibberellins (GAs) and auxins (Ozga and Reinecke, 2003). Auxin indole-3-acetic acid (IAA) can induce parthenocarpy in many horticultural plants, such as tomato, cucumber, and zucchini (Martinelli et al, 2009; Pomares-Viciana et al, 2017). Parthenocarpy can be controlled by a single gene, such as a transcriptional factor or a receptor in phytohormone signaling pathways

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