NnNF-YB1 induced by the potassium fertilizer enhances starch synthesis in rhizomes of Nelumbo nucifera

Lotus (Nelumbo nucifera Gaertn.) is one of the most important aquatic vegetables in China, which is rich in starch and is important sources of energy for livings. Potassium fertilizer has important effects on physiological characteristics, yield and quality of lotus rhizomes. However, the relationship between starch and potassium fertilizer remains unclear. Here, we investigated the relationship between starch quality and potassium fertilizer. Compared with the treatment without potassium fertilizer (CK), the total starch content, amylose content, and amylopectin content of potassium fertilizer treatment 30 kg/667 m2 (K30) were significantly increased. RNA-seq showed that K30 induces more than 2000 differentially expressed genes (DEGs), which mainly enriched in biosynthesis of starch and sucrose metabolism, secondary metabolites, photosynthesis. Meanwhile, K30 significantly promoted the expression of most of key genes and transcription factors involved in the regulation of starch synthesis. We identified a NF-YB transcription factor NnNF-YB1, induced by potassium fertilizer could activate the expression of NnGBSSII by directly bind to its promoter. Transient overexpression of NnNF-YB1 resulted in the increase of total starch, amylose and amylopectin content in rhizomes of lotus. NnNF-YB1 positively regulated the expression of NnGBSSII and plays an important role in starch synthesis under potassium fertilizer treatment. Collectively, our study provides a reference for fertilizer application in lotus production. At the same time, we revealed a new mechanism of potassium fertilizer increasing starch content and improving the quality of starch in rhizomes.