Chinese cabbage ( Brassica campestris L. ssp. pekinensis ) is a widely cultivated vegetable crop in eastern Asia. The flavor of Chinese cabbage was mostly affected by soluble sugar content. To make clear its accumulation and regulation mechanism, the content of different sugars in the internal blade (IB), the internal midrib (IM), the external blade (EB) and the external midrib (EM) of the leafy head were determined during the leafy head formation. The results showed that fructose was the major sugar accumulated in the internal tissues, followed by glucose. IM was the main tissue of sugar accumulation with the highest contents of total soluble sugar and hexose at harvest. RNA sequencing data of the four tissues at 90 DAS showed that the number of differentially expressed genes (DEGs) in IB and IM was the least (2408), while the number of DEGs between the external and internal tissues ranged from 6037 to 8674. The enzyme genes differentially expressed in ‘starch and sucrose metabolism’ pathway was detected during the leafy head development. The expression of two sucrose synthase (SUS) genes, SUS1a (Bra002332) and SUS1b (Bra006587), were always higher in IM than in the other tissues, and positively correlated with the content of total soluble sugar and hexose, respectively. SUS1 was considered to play an important role in leafy head development and sugar accumulation in Chinese cabbage.

中文翻译：

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大白菜（Brassica campestris L. ssp. pekinensis）叶状茎中糖分积累及代谢酶基因特征

大白菜（Brassica campestris L. ssp. pekinensis）是东亚地区广泛种植的蔬菜作物。大白菜的风味主要受可溶性糖含量的影响。为明确其积累和调节机制，测定了叶头内叶（IB）、内中脉（IM）、外叶（EB）和外中脉（EM）中不同糖类的含量。叶状头部形成。结果表明，果糖是体内组织中积累的主要糖分，其次是葡萄糖。IM是收获时总可溶性糖和己糖含量最高的糖类积累的主要组织。4种组织90 DAS的RNA测序数据显示，IB和IM中差异表达基因（DEGs）的数量最少（2408），而外部和内部组织之间的DEGs数量从6037到8674不等。在叶头发育过程中检测到在'淀粉和蔗糖代谢'途径中差异表达的酶基因。两种蔗糖合成酶（SUS）基因SUS1a（Bra002332）和SUS1b（Bra006587）在IM中的表达始终高于其他组织，分别与总可溶性糖和己糖含量呈正相关。SUS1被认为在大白菜的叶头发育和糖分积累中起重要作用。SUS1a（Bra002332）和SUS1b（Bra006587）在IM中总是高于其他组织，并且分别与总可溶性糖和己糖的含量呈正相关。SUS1被认为在大白菜的叶头发育和糖分积累中起重要作用。SUS1a（Bra002332）和SUS1b（Bra006587）在IM中总是高于其他组织，并且分别与总可溶性糖和己糖的含量呈正相关。SUS1被认为在大白菜的叶头发育和糖分积累中起重要作用。