Gibberellin biosynthesis is required for CPPU-induced parthenocarpy in melon

Abstract

Spraying N-(2-chloro-4-pyridyl)- N'-phenylurea (CPPU), an exogenous cytokinin (CK) growth regulator, is the conventional method for inducing fruit set during melon (Cucumis melo L.) production; however, the mechanism by which CPPU induces fruit set is unclear. Through histological and morphological observations, fruit size was comparable between CPPU-induced fruits and normal pollinated fruits because CPPU-induced fruits had higher cell density but smaller cell size compared with normal pollinated fruits. CPPU promotes the accumulation of gibberellin (GA) and auxin and decreases the level of abscisic acid (ABA) during fruit set. Moreover, application of the GA inhibitor paclobutrazol (PAC) partially inhibits CPPU-induced fruit set. Transcriptome analysis revealed that CPPU-induced fruit set specifically induced the GA-related pathway, in which the key synthase encoding gibberellin 20-oxidase 1 (CmGA20ox1) was specifically upregulated. Further study indicated that the two-component response regulator 2 (CmRR2) of the cytokinin signaling pathway, which is highly expressed at fruit setting, positively regulates the expression of CmGA20ox1. Collectively, our study determined that CPPU-induced melon fruit set is dependent on GA biosynthesis, providing a theoretical basis for the creation of parthenocarpic melon germplasm.

Acknowledgements

We thank Professor Huaisong Wang for providing ivf05 seeds. We also thank Biorun Bioscience Co., Ltd (Wuhan) for Dr Jin Jie’s contributions to the genetic transformation system of melon. This work was supported by the National Natural Science Foundation of China (32225044 to Z.Z., 32130093 to Z.Z., 32102404 to S.C., 32002064 to Y.L.), This work was also supported by the Taishan Scholar Foundation of the People’s Government of Shandong Province and the Natural Science Foundation of Shandong Province (ZR2020QC157).

Author contributions

Z.Z., S.C., and Y. Liu. designed the research. S.C., H.G., Y. Li., J.F., and H.W. performed the experiments and S.C. and Y. Liu. analyzed the data. B.L. revised the manuscript. Z.Z., S.C. and Y. Liu. wrote the manuscript. All authors participated in the research and approved the final manuscript.

Data availability

Relevant data can be found within the paper and its supporting materials. All data of this study are available from the corresponding author upon reasonable request.

Conflict of interest

All authors declare no conflict of interest.

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