Wang Cheng, Jiang Hongchao, Gao Ge, Yang Fan, Guan Jingyue, Qi Hongyan
College of Horticulture, Shenyang Agricultural University, Shenyang, 110866, China; Key Laboratory of Protected Horticulture of Education of Ministry and Liaoning Province, China; National & Local Joint Engineering Research Center of Northern Horticultural Facilities Design & Application Technology, Shenyang, 110866, China.
College of Horticulture, Shenyang Agricultural University, Shenyang, 110866, China; Key Laboratory of Protected Horticulture of Education of Ministry and Liaoning Province, China; National & Local Joint Engineering Research Center of Northern Horticultural Facilities Design & Application Technology, Shenyang, 110866, China.
Plant Physiol Biochem. 2023 Mar;196:361-369. doi: 10.1016/j.plaphy.2023.01.047. Epub 2023 Jan 25.
Sugar content is one of the determining factors for melon fruit maturity. Studies have shown that starch gradually degrades during fruit ripening, resulting in sugar accumulation. But the specific relationship between starch metabolism and sucrose accumulation was still unknown. Here, the starch and sugar contents, the activities of key enzymes and the expression patterns of genes related to starch-sucrose metabolism were determined in the fruit of high sugar and starch variety 'HS' and low sugar and starch variety 'LW'. It was found that starch accumulated during fruit development process, and then degraded at 30 days after anthesis (DAA), which was synchronized with sucrose accumulation in 'HS' fruit, while starch and sucrose contents were always at a lower level during 'LW' fruit maturation. Furthermore, starch metabolism-related enzymes (Adenine dinucleotide phosphate -glucose pyrophosphorylase (AGPase), α-amylase (AMY), β-amylase (BMY)) and the key enzymes for sucrose accumulation (sucrose phosphate synthase (SPS) and sucrose synthase (SS)) were significantly increased at ripening stage of 'HS' fruit, and their activities were consistent with the expressions of CmAPS2-2, CmAMY2, CmBAM1, CmBAM9 and CmSPS1. However, the contents of starch and sucrose and the activities of AGPase and SPS in 'LW' fruit didn't change significantly. We discovered an R2R3-type MYB transcription factor, CmMYB44, screened from yeast one hybrid library, could directly bind to the promoter of CmAPS2-2 to inhibit its transcription. These results revealed that the targeted down-regulation of CmAPS2-2 by CmMYB44 might be involved in the starch accumulation process, which affect the flavor quality of oriental melon fruit.
糖分含量是甜瓜果实成熟度的决定因素之一。研究表明，淀粉在果实成熟过程中逐渐降解，导致糖分积累。但淀粉代谢与蔗糖积累之间的具体关系仍不清楚。在此，测定了高糖高淀粉品种‘HS’和低糖低淀粉品种‘LW’果实中的淀粉和糖分含量、关键酶活性以及与淀粉-蔗糖代谢相关基因的表达模式。结果发现，淀粉在果实发育过程中积累，然后在开花后30天（DAA）降解，这与‘HS’果实中蔗糖的积累同步，而‘LW’果实成熟过程中淀粉和蔗糖含量始终处于较低水平。此外，淀粉代谢相关酶（腺苷二磷酸葡萄糖焦磷酸化酶（AGPase）、α-淀粉酶（AMY）、β-淀粉酶（BMY））和蔗糖积累关键酶（蔗糖磷酸合酶（SPS）和蔗糖合酶（SS））在‘HS’果实成熟阶段显著增加，其活性与CmAPS2-2、CmAMY2、CmBAM1、CmBAM9和CmSPS1的表达一致。然而，‘LW’果实中淀粉和蔗糖含量以及AGPase和SPS活性变化不显著。我们从酵母单杂交文库中筛选出一个R2R3型MYB转录因子CmMYB44，它可以直接结合到CmAPS2-2的启动子上抑制其转录。这些结果表明，CmMYB44对CmAPS2-2的靶向下调可能参与了淀粉积累过程，从而影响甜瓜果实的风味品质。
