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Article|01 May 2021|OPEN
Brassinosteroids suppress ethylene-induced fruitlet abscission through LcBZR1/2-mediated transcriptional repression of LcACS1/4 and LcACO2/3 in litchi
Xingshuai Ma1,2, Ye Yuan1,2, Caiqin Li1,2, Qian Wu1,2, Zidi He1,2, Jianguo Li2,1, & Minglei Zhao1,2,3,
1State Key Laboratory for Conservation and Utilization of Subtropical AgroBioresources, China Litchi Research Center, South China Agricultural University, 510642 Guangzhou, China
2Guangdong Litchi Engineering Research Center, College of Horticulture, South China Agricultural University, 510642 Guangzhou, China
3Ministry of Agriculture and Rural Affairs Key Laboratory of South China Horticultural Crop Biology and Germplasm Enhancement, College of Horticulture, South China Agricultural University, 510642 Guangzhou, China

Horticulture Research 8,
Article number: 105 (2021)
doi: 10.1038/hortres.2021.105
Views: 219

Received: 18 Aug 2020
Revised: 09 Feb 2021
Accepted: 22 Feb 2021
Published online: 01 May 2021

Abstract

Abscission in plants is tightly controlled by multiple phytohormones and the expression of various genes. However, whether the plant hormone brassinosteroids (BRs) are involved in this process is largely unknown. Here, we found that exogenous application of BRs reduced the ethylene-induced fruitlet abscission of litchi due to lower ethylene (ET) production and suppressed the expression of the ethylene biosynthetic genes LcACS1/4 and LcACO2/3 in the fruitlet abscission zone (FAZ). Two genes that encode the BR core signaling components brassinazole resistant (BZR) proteins, namely, LcBZR1 and LcBZR2, were characterized. LcBZR1/2 were localized to the nucleus and acted as transcription repressors. Interestingly, the LcBZR1/2 transcript levels were not changed during ET-induced fruitlet abscission, while their expression levels were significantly increased after BR application. Moreover, gel shift and transient expression assays indicated that LcBZR1/2 could suppress the transcription of LcACS1/4 and LcACO2/3 by specifically binding to their promoters. Importantly, ectopic expression of LcBZR1/2 in Arabidopsis significantly delayed floral organ abscission and suppressed ethylene biosynthesis. Collectively, our results suggest that BRs suppress ET-induced fruitlet abscission through LcBZR1/2-controlled expression of genes related to ethylene biosynthesis in litchi. In addition, similar results were observed in the Arabidopsis gain-of-function mutant bzr1-1D, which showed delayed floral organ abscission in parallel with lower expression of ACS/ACO genes and reduced ethylene production, suggesting that the mechanism of BZR-controlled organ abscission via regulation of ethylene biosynthesis might be conserved in Arabidopsis.