1. Academic Validation
  2. TRIPTYCHON-LIKE regulates aspects of both fruit flavor and color in citrus

TRIPTYCHON-LIKE regulates aspects of both fruit flavor and color in citrus

  • J Exp Bot. 2022 Jun 2;73(11):3610-3624. doi: 10.1093/jxb/erac069.
Jiaxian He 1 Yuantao Xu 1 Ding Huang 1 Jialing Fu 1 Ziang Liu 1 Lun Wang 1 Yin Zhang 1 Rangwei Xu 1 Li Li 2 3 Xiuxin Deng 1 4 Qiang Xu 1 4
Affiliations

Affiliations

  • 1 Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan 430070, China.
  • 2 Plant Breeding and Genetics Section, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853, USA.
  • 3 Robert W. Holley Center for Agriculture and Health, USDA-Agricultural Research Service, Cornell University, Ithaca, NY 14853, USA.
  • 4 Hubei Hongshan Laboratory, Wuhan 430070, China.
Abstract

Deciphering the genetic basis of organoleptic traits is critical for improving the quality of fruits, which greatly shapes their appeal to consumers. Here, we characterize the citrus R3-MYB transcription factor TRIPTYCHON-LIKE (CitTRL), which is closely associated with the levels of citric acid, proanthocyanidins (PAs), and anthocyanins. Overexpression of CitTRL lowered acidity levels and PA contents in citrus calli as well as anthocyanin and PA contents in Arabidopsis leaves and seeds. CitTRL interacts with the two basic helix-loop-helix (bHLH) proteins CitbHLH1 and ANTHOCYANIN 1 (CitAN1) to regulate fruit quality. We show that CitTRL competes with the R2R3-MYB CitRuby1 for binding to CitbHLH1 or CitAN1, thereby repressing their activation of anthocyanin structural genes. CitTRL also competes with a second R2R3-MYB, CitPH4, for binding to CitAN1, thus altering the expression of the vacuolar proton-pump gene PH5 and Leucoanthocyanidin reductase, responsible for vacuolar acidification and proanthocyanidins biosynthesis, respectively. Moreover, CitPH4 activates CitTRL transcription, thus forming an activator-repressor loop to prevent the overaccumulation of citric acid and PAs. Overall, this study demonstrates that CitTRL acts as a repressor of the accumulation of citric acid, PAs, and anthocyanins by a cross-regulation mechanism. Our results provide an opportunity to simultaneously manipulate these key traits as a means to produce citrus fruits that are both visually and organoleptically appealing.

Keywords

Activator–repressor loop; R3-MYB; anthocyanin; citric acid; citrus; negative regulator; proanthocyanidin.

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