Histological, hormonal and transcriptomic reveal the changes upon gibberellin-induced parthenocarpy in pear fruit

Abstract

Phytohormones play crucial roles in fruit set regulation and development. Here, gibberellins (GA4+7), but not GA3, induced pear parthenocarpy. To systematically investigate the changes upon GA4+7 induced pear parthenocarpy, dynamic changes in histology, hormone and transcript levels were observed and identified in unpollinated, pollinated and GA4+7-treated ovaries. Mesocarp cells continued developing in both GA4+7-treated and pollinated ovaries. In unpollinated ovaries, mesocarp cells stopped developing 14 days after anthesis. During fruit set process, GA4+7, but not GA1+3, increased after pollination. Abscisic acid (ABA) accumulation was significantly repressed by GA4+7 or pollination, but under unpollinated conditions, ABA was produced in large quantities. Moreover, indole-3-acetic acid biosynthesis was not induced by GA4+7 or pollination treatments. Details of this GA–auxin–ABA cross-linked gene network were determined by a comparative transcriptome analysis. The indole-3-acetic acid transport-related genes, mainly auxin efflux carrier component genes, were induced in both GA4+7-treated and pollinated ovaries. ABA biosynthetic genes of the 9-cis-epoxycarotenoid dioxygenase family were repressed by GA4+7 and pollination. Moreover, directly related genes in the downstream parthenocarpy network involved in cell division and expansion (upregulated), and MADS-box family genes (downregulated), were also identified. Thus, a model of GA-induced hormonal balance and its effects on parthenocarpy were established.

2,4‐D‐induced parthenocarpy in pear is mediated by enhancement of GA4 biosynthesis

“…In our study, 2,4‐D could induce cell division and expansion, and its effects were inhibited by PAC, indicating that GAs play key roles in 2,4‐D‐induced cell development. GAs have the reported capability to promote cell division and cell expansion (Liu et al , ). To investigate the relationships of 2,4‐D and GAs in cell developmental processes, we selected three related genes from our previous study (Liu et al ) in pear: Pbcyclin‐dependent kinase B2‐2 , Pbcyclin‐dependent kinase B2‐2‐like and Pbexpansin‐A10 .…”

“…GAs have the reported capability to promote cell division and cell expansion (Liu et al , ). To investigate the relationships of 2,4‐D and GAs in cell developmental processes, we selected three related genes from our previous study (Liu et al ) in pear: Pbcyclin‐dependent kinase B2‐2 , Pbcyclin‐dependent kinase B2‐2‐like and Pbexpansin‐A10 . In our previous study, GA treatment was able to promote the expressions of these three genes (Liu et al ).…”

“…To investigate the relationships of 2,4‐D and GAs in cell developmental processes, we selected three related genes from our previous study (Liu et al ) in pear: Pbcyclin‐dependent kinase B2‐2 , Pbcyclin‐dependent kinase B2‐2‐like and Pbexpansin‐A10 . In our previous study, GA treatment was able to promote the expressions of these three genes (Liu et al ). In the present study, their expression levels were significantly upregulated in the 2,4‐D‐only treatment group.…”

“…Liu et al () have indicated that active GA molecules (both GA 3 and GA 4 ) can induce parthenocarpy. In the present study, we determined the endogenous GA 3 , GA 4 and IAA contents of ovaries.…”

“…We thus hypothesize that the promotive effects of 2,4-D on cell development are mediated by GA content. Liu et al (2018) have indicated that active GA molecules (both GA 3 and GA 4 ) can induce parthenocarpy. In the present study, we determined the endogenous GA 3 , GA 4 and IAA contents of ovaries.…”