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Article|01 Jun 2019|OPEN
Comparative analysis of the transcriptomes of the calyx abscission zone of sweet orange insights into the huanglongbing-associated fruit abscission
Wei Zhao1 , Elizabeth A. Baldwin1 , , Jinhe Bai1 , Anne Plotto1 and Mike Irey,2
1USDA/ARS Horticultural Research Laboratory, 2001 South Rock Road, Fort Pierce, FL 34945, USA
2Southern Gardens Citrus Nursery, 111 Ponce de Leon Avenue, Clewiston, FL 33440, USA
*Corresponding author. E-mail: liz.baldwin@ars.usda.gov

Horticulture Research 6,
Article number: 71 (2019)
doi: https://doi.org/10.1038/s41438-019-0152-4
Views: 1022

Received: 16 May 2018
Revised: 08 Apr 2019
Accepted: 10 Apr 2019
Published online: 01 Jun 2019

Abstract

Citrus greening disease or huanglongbing (HLB) is associated with excessive pre-harvest fruit drop. To understand the mechanisms of the HLB-associated fruit abscission, transcriptomes were analyzed by RNA sequencing of calyx abscission zones (AZ-C) of dropped “Hamlin” oranges from HLB-diseased trees upon shaking the trees (Dd), retained oranges on diseased trees (Rd), dropped oranges from healthy shaken trees (Dh), and retained oranges on healthy trees (Rh). Cluster analysis of transcripts indicated that Dd had the largest distances from all other groups. Comparisons of transcriptomes revealed 1047, 1599, 813, and 764 differentially expressed genes (DEGs) between Dd/Rd, Dd/Dh, Dh/Rh, and Rd/Rh. The gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses indicated hormone signaling, defense response, and secondary metabolism were involved in HLB-associated fruit abscission. Ethylene (ET) and jasmonic acid (JA) synthesis/signaling-related genes were upregulated in Dd, while other phytohormone-related genes were generally downregulated. In addition, genes related to JA/ET-activated defense response were upregulated in Dd as well. Consistent with the phytohormone gene expression data, increased levels (p < 0.05) of ET and JA, and a decreased level (p < 0.05) of abscisic acid were found in Dd compared with Rd, Dh or Rh. Lasiodiploidia theobromae level in Dd AZ-C was higher than the other fruit types, confirmed by qPCR, indicating AZ-C secondary fungal infection of HLB fruit may exacerbate their abscission. This information will help formulate effective strategies to control HLB-related abscission.