A subtilisin-like serine protease essential for mucilage release from Arabidopsis seed coats
A subtilisin-like serine protease essential for mucilage release from Arabidopsis seed coats
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DOI：
10.1111/j.1365-313x.2008.03437.x
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发表时间：
2008-05-01
期刊：
影响因子：
7.2
通讯作者：
Altmann, Thomas
中科院分区：
文献类型：
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作者：
Rautengarten, Carsten;Usadel, Bjoern;Altmann, Thomas
在拟南芥种子发育过程中，由果胶组成的大量粘液沉积在种皮外壁下的外质体中。成熟种子被吸胀后，储存的粘液通过水合作用膨胀，打破包裹整个种子的外细胞壁。携带AtSBT1.7功能缺失等位基因的突变种子，编码56种拟南芥枯草样丝氨酸蛋白酶（枯草酶）中的一种，在水合作用下不释放粘液。对突变种皮的显微分析显示，与野生型种子相比，突变种皮的结构没有明显的差异。用阳离子螯合剂弱化外主壁；触发了变种人种皮上的粘液释放。然而，与成熟的野生型种子相比，突变体的外细胞壁没有在种皮表皮细胞的径向壁破裂，而是在种子的合点端打开，并整体释放。在图1.7中，鼠李糖总含量和半乳糖醛酸含量与野生型种子相比保持不变，而鼠李糖和半乳糖醛酸是粘液的主干。因此，在atsbt1.7突变体中，挤压和溶解度，而不是粘液的初始沉积受到影响。AtSBT1.7定位于发育中的种皮，表明在种皮发育或成熟中起作用。外种皮破裂和粘液释放模式的改变表明，AtSBT1.7触发了细胞壁修饰酶的积累和/或激活，这些酶是使外原代细胞壁松动或促进粘液膨胀所必需的，正如AtSBT1.7突变体种子中果胶甲基酯酶活性升高所表明的那样。
During Arabidopsis seed development large quantities of mucilage, composed of pectins, are deposited into the apoplast underneath the outer wall of the seed coat. Upon imbibition of mature seeds, the stored mucilage expands through hydration and breaks the outer cell wall that encapsulates the whole seed. Mutant seeds carrying loss-of-function alleles of AtSBT1.7 that encodes one of 56 Arabidopsis thaliana subtilisin-like serine proteases (subtilases) do not release mucilage upon hydration. Microscopic analysis of the mutant seed coat revealed no visible structural differences compared with wild-type seeds. Weakening of the outer primary wall using cation chelators; triggered mucilage release from the seed coats of mutants. However, in contrast to mature wild-type seeds, the mutant's outer cell walls did not rupture at the radial walls of the seed coat epidermal cells, but instead opened at the chalazal end of the seed, and were released in one piece. In atsbt1.7, the total rhamnose and galacturonic acid contents, representing the backbone of mucilage, remained unchanged compared with wild-type seeds. Thus, extrusion and solubility, but not the initial deposition of mucilage, are affected in atsbt1.7 mutants. AtSBT1.7 is localized in the developing seed coat, indicating a role in testa development or maturation. The altered mode of rupture of the outer seed coat wall and mucilage release indicate that AtSBT1.7 triggers the accumulation, and/or activation, of cell wall modifying enzymes necessary either for the loosening of the outer primary cell wall, or to facilitate swelling of the mucilage, as indicated by elevated pectin methylesterase activity in developing atsbt1.7 mutant seeds.