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Article|01 Oct 2021|OPEN
The NAC transcription factor ClNAC68 positively regulates sugar content and seed development in watermelon by repressing ClINV and ClGH3.6
Jinfang Wang1, Jie Zhang1, Yi Ren1, Maoying Li1, Shaowei Tian1, Yongtao Yu1, Yi Zuo1, Guoyi Gong1, Yong Xu1, Yanping Wang1,, Haiying Zhang1, & Shaogui Guo1,
1 National Watermelon and Melon Improvement Center, Beijing Academy of Agricultural and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China

Horticulture Research 8,
Article number: 214 (2021)
doi: 10.1038/hortres.2021.214
Views: 60

Received: 18 Jan 2021
Revised: 31 May 2021
Accepted: 15 Jun 2021
Published online: 01 Oct 2021

Abstract

NAC (NAM, ATAF1/2, and CUC2) transcription factors play important roles in fruit ripening and quality. The watermelon genome encodes 80 NAC genes, and 21 of these NAC genes are highly expressed in both the flesh and vascular tissues. Among these genes, ClNAC68 expression was significantly higher in flesh than in rind. However, the intrinsic regulatory mechanism of ClNAC68 in fruit ripening and quality is still unknown. In this study, we found that ClNAC68 is a transcriptional repressor and that the repression domain is located in the C-terminus. Knockout of ClNAC68 by the CRISPR-Cas9 system decreased the soluble solid content and sucrose accumulation in mutant flesh. Development was delayed, germination was inhibited, and the IAA content was significantly decreased in mutant seeds. Transcriptome analysis showed that the invertase gene ClINV was the only gene involved in sucrose metabolism that was upregulated in mutant flesh, and expression of the indole-3-acetic acid-amido synthetase gene ClGH3.6 in the IAA signaling pathway was also induced in mutant seeds. EMSA and dual-luciferase assays showed that ClNAC68 directly bound to the promoters of ClINV and ClGH3.6 to repress their expression. These results indicated that ClNAC68 positively regulated sugar and IAA accumulation by repressing ClINV and ClGH3.6. Our findings provide new insights into the regulatory mechanisms by which NAC transcription factors affect fruit quality and seed development.