Proanthocyanidins (PAs) are major defense-related phenolics in mulberry, but the mechanism underlying their biosynthesis remains uncharacterized. In this study, the relationship between the expression of genes encoding anthocyanidin reductase (ANR) or leucoanthocyanidin reductase (LAR) and PA biosynthesis was investigated in white and red mulberry fruits. In ripening fruits, the MnANR and MnLAR transcription levels tended to decrease, whereas the catechin and epicatechin contents initially increased and then decreased. In contrast, the PA content exhibited a clearly different trend. The ectopic expression of MnANR and MnLAR in tobacco increased the resistance to Botrytis cinerea, as evidenced by the less extensive disease symptoms of the transgenic plants compared with the wild-type plants. In vitro experiments revealed that the transgenic tobacco crude leaf extract had an obvious inhibitory effect on B. cinerea. Moreover, the ectopic expression of MnANR and MnLAR in tobacco inhibited the expression of anthocyanin biosynthesis genes, resulting in decreased anthocyanin contents in flowers. The results of this study may be useful for elucidating the mechanism underlying PA biosynthesis. Furthermore, ANR and LAR represent potential targets for improving the resistance of mulberry and related plant species to B. cinerea.

中文翻译：

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桑葚基因 MnANR 和 MnLAR 赋予转基因植物对灰霉病的抗性


原花青素（PA）是桑葚中主要的防御相关酚类物质，但其生物合成的机制仍不清楚。在这项研究中，研究了白色和红色桑椹果实中编码花青素还原酶（ANR）或无色花青素还原酶（LAR）的基因的表达与PA生物合成之间的关系。在成熟果实中，MnANR和MnLAR转录水平呈下降趋势，而儿茶素和表儿茶素含量先上升后下降。相比之下，PA含量表现出明显不同的趋势。烟草中 MnANR 和 MnLAR 的异位表达增加了对灰霉病菌的抗性，与野生型植物相比，转基因植物的疾病症状较不广泛就证明了这一点。体外实验表明，转基因烟草粗叶提取物对灰霉病菌具有明显的抑制作用。此外，烟草中MnANR和MnLAR的异位表达抑制了花青素生物合成基因的表达，导致花朵中花青素含量下降。这项研究的结果可能有助于阐明 PA 生物合成的机制。此外，ANR 和 LAR 代表了提高桑树和相关植物物种对灰霉病的抗性的潜在目标。