Li Jinyan, Lu Yao, Cheng Ke, Zhu Guoning, Wang Xiaoyi, Lin Tao, Zhang Bo, Ma Liqun, Qu Guiqin, Zhu Benzhong, Fu Daqi, Luo Yunbo, Zhu Hongliang
The College of Food Science and Nutritional Engineering, China Agricultural University, Beijing, 100083, China.
The College of Horticulture, China Agricultural University, Beijing, 100094, China.
Plant J. 2025 Mar;121(5):e70043. doi: 10.1111/tpj.70043.
In the climacteric fruit tomato (Solanum lycopersicum), 1-aminocyclopropane-1-carboxylic acid (ACC) synthase 2 (ACS2) and ACS4 are jointly recognized as key enzymes in orchestrating System-2 ethylene biosynthesis during fruit ripening. However, the precise roles and individual contributions of ACS2 and ACS4 within this process remain elusive. Here, we generate acs2, acs4 single knockout, and acs2/4 double knockout mutants through the CRISPR/Cas9 system. Our results reveal that the knockout of ACS2 leads to a modest decrease in ethylene production, with minimal effects on fruit ripening. In contrast, the knockout of ACS4 unveils a severe ripening defect akin to that observed in the acs2/4 mutant, which stems from a profound disruption of ethylene autocatalytic biosynthesis, ultimately resulting in inadequate ethylene production vital for supporting fruit ripening. Transcriptome analysis, in conjunction with exogenous ethylene treatment, conclusively demonstrates a pronounced dose-dependent correlation between fruit ripening and ethylene, wherein varying doses of ethylene distinctly regulate the expression of a substantial number of ripening-related genes, eventually controlling both the ripening process and quality formation. These findings clarify the pivotal role of ACS4 in ethylene biosynthesis compared to ACS2 and deepen our understanding of the fine-tuned regulation of ethylene in climacteric fruit ripening.
在跃变型果实番茄（茄属番茄）中，1-氨基环丙烷-1-羧酸（ACC）合酶2（ACS2）和ACS4被共同认为是果实成熟过程中协调系统2乙烯生物合成的关键酶。然而，ACS2和ACS4在此过程中的具体作用和各自贡献仍不清楚。在此，我们通过CRISPR/Cas9系统生成了acs2、acs4单基因敲除突变体和acs2/4双基因敲除突变体。我们的结果表明，敲除ACS2会导致乙烯产量适度下降，对果实成熟影响最小。相比之下，敲除ACS4会出现类似于acs2/4突变体中观察到的严重成熟缺陷，这是由于乙烯自催化生物合成的严重破坏，最终导致支持果实成熟所需的乙烯产量不足。转录组分析结合外源乙烯处理，最终证明果实成熟与乙烯之间存在明显的剂量依赖性相关性，其中不同剂量的乙烯明显调节大量成熟相关基因的表达，最终控制成熟过程和品质形成。这些发现阐明了与ACS2相比，ACS4在乙烯生物合成中的关键作用，并加深了我们对跃变型果实成熟过程中乙烯精细调控的理解。
