Browse Articles

Article|01 Mar 2021|OPEN
Cytokinin but not gibberellin application had major impact on the phenylpropanoid pathway in grape
Kamal Tyagi1,2, Itay Maoz1, Bettina Kochanek1, Noa Sela3, Larry Lerno2,4, Susan E. Ebeler 2 & Amnon Lichter 1
1Department of Postharvest Science, Agricultural Research Organization, The Volcani Center, Rishon LeZion, Israel
2Department of Viticulture and Enology, University of California, Davis, CA 95616, USA
3Department of Plant Pathology, Agricultural Research Organization, The Volcani Center, Rishon LeZion, Israel
4Food Safety and Measurement Facility, University of California, Davis, CA 95616, USA

Horticulture Research 8,
Article number: 51 (2021)
doi: 10.1038/hortres.2021.51
Views: 257

Received: 26 Sep 2020
Revised: 05 Jan 2021
Accepted: 11 Jan 2021
Published online: 01 Mar 2021

Abstract

Cytokinin and gibberellic acid (GA) are growth regulators used to increase berry size in seedless grapes and it is of interest to understand their effects on the phenylpropanoid pathway and on ripening processes. GA3 and synthetic cytokinin forchlorfenuron (N-(2-chloro-4-pyridyl)-N′-phenylurea, CPPU) and their combination were applied to 6 mm diameter fruitlets of ‘Sable Seedless’, and berries were sampled 51 and 70 days (d) following application. All treatments increased berry size and delayed sugar accumulation and acid degradation with a stronger effect of CPPU. CPPU, but not GA, reduced berry color and the levels of anthocyanins. While CPPU reduced the levels of anthocyanins by more than 50%, the combined treatment of GA+CPPU reduced the levels by about 25% at 51 d. CPPU treatment had minor effects on flavonols content but increased the levels of monomeric flavan-3-ols by more than two-fold. Phloroglucinol analysis using HPLC showed that proanthocyanidin content was significantly increased by CPPU, whereas mean degree of polymerization was reduced from 26 to 19. Volatile analysis by GC-MS showed changes in composition with CPPU or GA treatment with potential impact on flavor. RNA-seq analysis showed that GA had a minor overall effect on the transcriptome whereas CPPU had pronounced effects on gene expression at both 51 and 70 d. Comparing the control and CPPU at similar Brix of ca. 19.7°, a reduced expression of stilbene synthases (STSs) including their regulators MYB14 and MYB15, and other phenylpropanoid-related genes was observed in CPPU-treated grapes. Overall, our study shows that CPPU had a major influence on the phenylpropanoid pathway and affected multiple ripening-related processes.