甘薯块根发育过程中关键蔗糖分解酶及其基因家族成员的鉴定

蔗糖分解酶在马铃薯和胡萝卜等块根/块茎的生长发育中发挥着重要作用,但在甘薯块根发育中的作用机制尚不清楚。本研究以2个在块根数量和鲜重上存在显著差异的甘薯品种‘高系14'及其突变体为材料,对其不同发育时期（30、60、90、120 d）块根中的可溶性糖（蔗糖、葡萄糖和果糖）、淀粉含量、蔗糖分解酶活性以及相关基因家族成员的表达水平进行测定,以明确调控块根数量和大小的关键蔗糖分解酶及主要基因家族成员。结果表明：（1）阐明了4种蔗糖分解酶活性在薯块根发育过程中的变化规律,细胞质转化酶（CIN）和液泡转化酶（VIN）活性的整体变化趋势呈现‘u'形曲线,即块根发育早期、晚期活性相对较高,发育中期最低;细胞壁转化酶（CWIN）和蔗糖合成酶（Sus）活性整体变化趋势呈‘n'形曲线,与前者正好相反,即在块根发育早期、晚期较低,发育中期最高。（2）和突变体相比,具有较高块根数量和鲜重的‘高系14'在块根发育早期（30 d）具有较高的Sus和CIN活性,而高Sus和CIN活性可以促进蔗糖由叶片向块根转运,从而提高块根中的淀粉、蔗糖和葡萄糖含量,最终为块根的生长发育提供能量和碳骨架以增加块根数量和鲜重。（3）从甘薯基因组中共鉴定出9个Sus基因家族成员和12个CIN基因家族成员,其中有1个Sus基因（IbSus6）和5个CIN基因（IbCIN4、IbCIN6、IbCIN8、IbCIN10和IbCIN11）的表达水平在30 d时表现为‘高系14'显著高于突变体,同时IbSus6和IbCIN4、IbCIN8、IbCIN10、IbCIN11分别为30 d块根中表达的主要Sus和CIN基因家族成员,因此上述1个Sus基因家族成员和4个CIN基因家族成员可能是调控甘薯块根发育的主要蔗糖分解酶基因。总之,Sus和CIN在甘薯块根早期发育中发挥着重要作用,其关键基因家族成员的阐明可为优异甘薯新品种的选育提供理论依据。

Identification of Key Sucrose-degrading Enzymes and the Relevant Gene Family Members in the Development of Sweetpotato Storage Roots

Sucrose catabolism plays important roles in the development of potato tuberous roots and carrot taproots, but the roles of sucrose catabolism in the development of sweetpotato storage roots remain elusive. In this paper, two sweetpotato lines ‘Kokei 14' and the mutant were employed in the research, which have significant differences in the storage root number per plant and fresh weight per storage root. In order to identify the key sucrose-degrading enzymes and the relevant gene family members that regulate the number and size of storage roots, the content of soluble sugar (sucrose, glucose and fructose) and starch, the activities of four sucrose-degrading enzymes and the expression level of the genes were measured at different development stages (30 d, 60 d, 90 d and 120 d) of the storage roots of the two sweet potato lines. The results are as follows: (1) The dynamic changes of the activities of four sucrose-degrading enzymes during the development of storage roots were clarified. The overall change trend of cytoplasmic invertase (CIN) and vacuolar invertase (VIN) activities showed a ‘u' curve, i.e. the activities were relatively higher in the early and late stages of development, but the lowest in the middle stage of development; The overall change trend of cell wall invertase (CWIN) and sucrose synthase (Sus) were just reverse and showed an ‘n' curve, i.e. the activities were relative lower in the early and late stage of storage root development, and were the highest in the middle stage of development. (2) As compared with the mutant, ‘Kokei 14' with higher number and fresh weight of storage roots had higher Sus and CIN activities in the early stage of storage root development (30 d), and higher Sus and CIN activities could promote the transport of sucrose from leaves to storage roots, and consequently increase the content of starch, sucrose and glucose in storage roots, which finally provided energy and carbon skeleton for the development of root tubers to increase the number and fresh weight of storage roots. (3) Nine Sus gene family members and twelve CIN gene family members were identified from the sweet potato genome. Among them, the expression levels of one Sus gene (IbSus6) and five CIN genes (IbCIN4, IbCIN6, IbCIN8, IbCIN10 and IbCIN11) were significantly higher in 30 d of storage roots of ‘Kokei 14' than in that of the mutant. Furthermore, IbSus6 and IbCIN4, IbCIN8, IbCIN10, IbCIN11were the main members of Sus and CIN gene family expressed in 30 d storage roots, respectively. Therefore, the Sus gene and four CIN genes may be the key genes regulating the development of sweet potato storage roost. In conclusion, Sus and CIN play important roles in the early developmental stage of of sweet potato storage roots and identification of the key gene family members can provide a theoretical basis for the breeding of excellent new sweetpotato varieties.