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

Abstract

Parthenocarpy, the productions of seedless fruit without pollination or fertilization, is a potentially desirable trait in many commercially grown fruits, especially in pear, which is self-incompatible. Phytohormones play important roles in fruit set, a process crucial for parthenocarpy. In this study, 2,4-dichlorophenoxyacetic acid (2,4-D), an artificially synthesized plant growth regulator with functions similar to auxin, was found to induce parthenocarpy in pear. Histological observations revealed that 2,4-D promoted cell division and expansion, which increased cortex thickness, but the effect was weakened by paclobutrazol (PAC), a gibberellin (GA) biosynthesis inhibitor. Phenotypic differences in pear may therefore be due to different GA contents. Hormone testing indicated that 2,4-D mainly induced the production of bioactive GA , rather than GA Three key oxidase genes function in the GA biosynthetic pathway: GA20ox, GA3ox and GA2ox. In a pear group treated with only 2,4-D, PbGA20ox2-like and PbGA3ox-1 were significantly upregulated. When treated with 2,4-D supplemented with PAC, however, expression levels of these genes were significantly downregulated. Additionally, PbGA2ox1-like and PbGA2ox2-like expression levels were significantly downregulated in pear treated with either 2,4-D only or 2,4-D supplemented with PAC. We thus hypothesize that 2,4-D can induce parthenocarpy by enhancing GA biosynthesis.

PbGA20ox2 Regulates Fruit Set and Induces Parthenocarpy by Enhancing GA4 Content

“…Plant hormones play key roles in parthenocarpic fruit growth. Parthenocarpy can be induced by the exogenous application of plant hormones, such as gibberellins (GAs), auxins, and melatonin (Cong et al, 2018;Liu et al, 2018a;Liu et al, 2018b), as well as the regulation of endogenous hormone contents (Mesejo et al, 2010;Ding et al, 2013;Sugiyama et al, 2014;Niu et al, 2015). Application of GAs can be used for this purpose in many horticultural plants, such as apple (Watanabe et al, 2008), loquat (Aslmoshtaghi and Shahsavar, 2013) and pear (Liu et al, 2018b).…”

Transcriptomic and metabolomic analysis provides insights into anthocyanin and procyanidin accumulation in pear

“…Phytohormones play important roles in young fruit development. Young pear fruits contain high level of auxin, and low level of ethylene [49]. Further functional analyses of PcERF003 and PcIAA13 may help to elucidate the links between the effects of auxin and ethylene on anthocyanin and/or PA accumulation in young developing pear fruit.…”

CPPU may induce gibberellin-independent parthenocarpy associated with PbRR9 in ‘Dangshansu’ pear

“…In tomato, CPPU-induced parthenocarpy is partly dependent on enhanced gibberellin and auxin biosynthesis and the application of PAC can significantly decrease gibberellin content 30 . Our previous studies have indicated that GA 4+7 , 2,4-dichlorophenoxyacetic acid (2,4-D), and melatonin (MT) can all induce parthenocarpy, which in pear is dependent on gibberellin 12,24,35 . To investigate whether gibberellin also plays a key role in CPPU-induced parthenocarpy in pear, we sprayed CPPU supplemented with PAC (a gibberellin synthesis inhibitor) on bagged 'Dangshansu' pear flowers.…”

“…Auxin was the first phytohormone discovered to induce parthenocarpy in plants 7,8 . Previous studies have indicated that an ectopic supply of auxin or auxin-like substances can induce parthenocarpy in strawberry 9 , tomato 10 , pear 11,12 , and eggplant 13 . In addition, changes in auxin biosynthesis and signaling pathways have been shown to induce parthenocarpic fruit set and fruit development.…”

“…Similar to auxin-related parthenocarpy, RNAi silencing of DELLA-the key repressor of the gibberellin signaling pathway-can induce parthenocarpic fruit development 28 . Crosstalk between auxin and gibberellin has been reported in tomato and pear, with auxin being upstream of gibberellin in parthenocarpy 10,12 .…”