Carotenoids are a class of bioactive compounds that exhibit health-promoting properties for humans, but their regulation in bananas during fruit ripening remains largely unclear. Here, we found that the total carotenoid content continued to be elevated along the course of banana ripening and peaked at the ripening stage followed by a decrease, which is presumably caused by the transcript abundances of carotenoid biosynthetic genes MaLCYB1.1 and MaLCYB1.2. Moreover, a ripening-inducible transcription factor MaSPL16 was characterized, which was a nuclear protein with transactivation activity. Transient transformation of MaSPL16 in banana fruits led to enhanced transcript levels of MaLCYB1.1 and MaLCYB1.2 and hence the total carotenoid accumulation. Importantly, MaSPL16 stimulated the transcription of MaLCYB1.1 and MaLCYB1.2 through directly binding to their promoters. Collectively, our findings indicate that MaSPL16 behaves as an activator to modulate banana carotenoid biosynthesis, which may provide a new target for molecular improvement of the nutritional and bioactive qualities of agricultural crops that accumulate carotenoids.

中文翻译：

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香蕉MaSPL16通过激活番茄红素β-环化酶基因的转录来调节果实成熟过程中的类胡萝卜素生物合成。

类胡萝卜素是一类生物活性化合物，对人类具有促进健康的特性，但是在水果成熟期间它们在香蕉中的调节作用仍然不清楚。在这里，我们发现总的类胡萝卜素含量在香蕉成熟过程中继续升高，并在成熟阶段达到峰值，然后下降，这可能是由于类胡萝卜素生物合成基因MaLCYB1.1和MaLCYB1.2的转录本丰度引起的。此外，表征了成熟诱导型转录因子MaSPL16，它是具有反式激活活性的核蛋白。香蕉果实中MaSPL16的瞬时转化导致MaLCYB1.1和MaLCYB1.2的转录水平提高，从而导致总类胡萝卜素积累。重要的是，MaSPL16刺激了MaLCYB1.1和MaLCYB1的转录。2通过直接与其启动子结合。总的来说，我们的发现表明，MaSPL16充当调节香蕉类胡萝卜素生物合成的激活剂，这可能为提高积累类胡萝卜素的农作物的营养和生物活性品质提供新的目标。