郝兆东
the plant journal:油菜细胞壁转化酶BrCWINV4A控制花蜜量和糖组成
2021-8-3 10:44
阅读:1787

A cell wall invertase controls nectar volume and sugar composition

第一作者Anzu Minami

第一单位明尼苏达大学

通讯作者Clay J. Carter


 Abstract 


大背景Nectar volume and sugar composition are key determinants of the strength of plant–pollinator mutualisms. The main nectar sugars are sucrose, glucose and fructose, which can vary widely in ratio and concentration across species.


小背景Brassica spp. produce a hexose-dominant nectar (high in the monosaccharides glucose and fructose) with very low levels of the disaccharide sucrose. Cell wall invertases (CWINVs) catalyze the irreversible hydrolysis of sucrose into glucose and fructose in the apoplast. 


结果1-表达模式:We found that BrCWINV4A is highly expressed in the nectaries of Brassica rapa


结果2-功能缺失突变表型:Moreover, a brcwinv4a null mutant: (i) has greatly reduced CWINV activity in the nectaries; (ii) produces a sucrose-rich nectar; but (iii) with significantly less volume. These results definitively demonstrate that CWINV activity is not only essential for the production of a hexose-rich nectar, but also support a hypothetical model of nectar secretion in which its hydrolase activity is required for maintaining a high intracellular-to-extracellular sucrose ratio that facilitates the continuous export of sucrose into the nectary apoplast. 


结果3-花蜜滴:The extracellular hydrolysis of each sucrose into two hexoses by BrCWINV4A also likely creates the osmotic potential required for nectar droplet formation. These results cumulatively indicate that modulation of CWINV activity can at least partially account for naturally occurring differences in nectar volume and sugar composition. 


结果4-蜜蜂访花:Finally, honeybees prefer nectars with some sucrose, but wild-type B. rapa flowers were much more heavily visited than flowers of brcwinv4a, suggesting that the potentially attractive sucrose-rich nectar of brcwinv4a could not compensate for its low volume.


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 摘 要 


花蜜量和糖组成是决定植物-传粉者之间共生关系牢固性的关键因素。主要的花蜜糖是蔗糖、葡萄糖和果糖,它们的比例和浓度因物种而异。芸苔属植物的花蜜糖是以己糖为主(单糖类的葡萄糖和果糖含量最高),而二糖类的蔗糖含量极低。细胞壁转化酶(CWINVs)在质外体中催化蔗糖不可逆水解为葡萄糖和果糖。作者发现BrCWINV4A在油菜的蜜腺中表达量较高。此外,brcwinv4a无义突变体表现出:(i)蜜腺中CWINV活性大大降低;(ii)产生了富含蔗糖的花蜜;(iii)花蜜量明显减少。这些结果明确表明,CWINV活性不仅有助于产生富含己糖的花蜜,同时也支持花蜜分泌的假设模型,该模型中水解酶活性是维持胞内与胞外高蔗糖比所必需的,这有助于蔗糖持续输出到蜜腺质外体。BrCWINV4A将每个蔗糖分子在胞外水解成两个己糖,这可能产生了形成花蜜滴所需的渗透势。这些结果表明,CWINV活性的调节至少可以部分解释花蜜量和糖组成的自然差异。最后,蜜蜂偏爱含有一些蔗糖的花蜜,但与brcwinv4a的花朵相比,野生型油菜的访花量更大,这表明brcwinv4a富有吸引力的含蔗糖花蜜无法弥补其花蜜较量的缺陷。


 通讯作者 

** Clay J. Carter **


研究方向:植物-微生物互作、植物-动物互作以及植物细胞中的蛋白质运输。


doi:  https://doi.org/10.1111/tpj.15357


Journal: the plant journal

Published online: July 29, 2021

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