CRISPR/Cas9-mediated SNAC9 mutants reveal the positive regulation of tomato ripening by SNAC9 and the mechanism of carotenoid metabolism regulation

Yuan Feng; Xiaohong Kou; Shuai Yuan; Caie Wu; Xiaoyang Zhao; Zhaohui Xue; Qingxiu Li; Zhengyu Huang; Yijie Sun

doi:10.1093/hr/uhad019

CRISPR/Cas9-mediated SNAC9 mutants reveal the positive regulation of tomato ripening by SNAC9 and the mechanism of carotenoid metabolism regulation

Hortic Res. 2023 Feb 10;10(4):uhad019. doi: 10.1093/hr/uhad019. eCollection 2023 Apr.

Authors

Yuan Feng¹, Xiaohong Kou¹, Shuai Yuan¹, Caie Wu², Xiaoyang Zhao¹, Zhaohui Xue¹, Qingxiu Li³, Zhengyu Huang¹, Yijie Sun¹

Affiliations

¹ School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China.
² College of Light Industry and Food Engineering, Nanjing Forestry University, Nanjing 210037, China.
³ College of Food Science and Biological Engineering, Tianjin Agricultural University, Tianjin 300384, China.

Abstract

NAC transcriptional regulators are crucial for tomato ripening. Virus-induced gene silencing (VIGS) of SNAC9 (SlNAC19, Gene ID: 101248665) affects tomato ripening, and SNAC9 is involved in ethylene and abscisic acid (ABA) metabolic pathways. However, the function of SNAC9 in pigment metabolism in tomatoes remains unclear. This work seeks to discover the mechanism of SNAC9 involvement in pigment metabolism during tomato ripening by establishing a SNAC9 knockout model using CRISPR/Cas9 technology. The results indicated that fruit ripening was delayed in knockout (KO) mutants, and SNAC9 mutation significantly affected carotenoid metabolism. The chlorophyll (Chl) degradation rate, total carotenoid content, and lycopene content decreased significantly in the mutants. The transformation rate of chloroplasts to chromoplasts in mutants was slower, which was related to the carotenoid content. Furthermore, SNAC9 changed the expression of critical genes (PSY1, PDS, CRTISO, Z-ISO, SGR1, DXS2, LCYE, LCYB, and CrtR-b2) involved in pigment metabolism in tomato ripening. SNAC9 knockout also altered the expression levels of critical genes involved in the biosynthesis of ethylene and ABA. Accordingly, SNAC9 regulated carotenoid metabolism by directly regulating PSY1, DXS2, SGR1, and CrtR-b2. This research provides a foundation for developing the tomato ripening network and precise tomato ripening regulation.