Chen F, Dahal P, Bradford K J
Department of Vegetable Crops, One Shields Avenue, University of California, Davis, CA 95616-8631, USA.
Plant Physiol. 2001 Nov;127(3):928-36.
Expansins are plant proteins that can induce extension of isolated cell walls and are proposed to mediate cell expansion. Three expansin genes were expressed in germinating tomato (Lycopersicon esculentum Mill.) seeds, one of which (LeEXP4) was expressed specifically in the endosperm cap tissue enclosing the radicle tip. The other two genes (LeEXP8 and LeEXP10) were expressed in the embryo and are further characterized here. LeEXP8 mRNA was not detected in developing or mature seeds but accumulated specifically in the radicle cortex during and after germination. In contrast, LeEXP10 mRNA was abundant at an early stage of seed development corresponding to the period of rapid embryo expansion; it then decreased during seed maturation and increased again during germination. When gibberellin-deficient (gib-1) mutant seeds were imbibed in water, LeEXP8 mRNA was not detected, but a low level of LeEXP10 mRNA was present. Expression of both genes increased when gib-1 seeds were imbibed in gibberellin. Abscisic acid did not prevent the initial expression of LeEXP8 and LeEXP10, but mRNA abundance of both genes subsequently decreased during extended incubation. The initial increase in LeEXP8, but not LeEXP10, mRNA accumulation was blocked by low water potential, but LeEXP10 mRNA amounts fell after longer incubation. When seeds were transferred from abscisic acid or low water potential solutions to water, abundance of both LeEXP8 and LeEXP10 mRNAs increased in association with germination. The tissue localization and expression patterns of both LeEXP8 and LeEXP10 suggest developmentally specific roles during embryo and seedling growth.
扩展蛋白是一类能诱导离体细胞壁伸展的植物蛋白，被认为在细胞扩张过程中起介导作用。三个扩展蛋白基因在萌发的番茄（Lycopersicon esculentum Mill.）种子中表达，其中一个基因（LeEXP4）在包裹胚根尖端的胚乳帽组织中特异性表达。另外两个基因（LeEXP8和LeEXP10）在胚中表达，本文将对它们进行进一步的特性分析。在发育中的种子或成熟种子中未检测到LeEXP8 mRNA，但在萌发期间及之后，它在胚根皮层中特异性积累。相比之下，LeEXP10 mRNA在种子发育早期丰富，对应于胚快速扩张的时期；然后在种子成熟期间减少，在萌发期间再次增加。当赤霉素缺陷型（gib-1）突变体种子吸水时，未检测到LeEXP8 mRNA，但存在低水平的LeEXP10 mRNA。当gib-1种子在赤霉素中吸水时，两个基因的表达均增加。脱落酸并未阻止LeEXP8和LeEXP10的初始表达，但在延长培养期间，两个基因的mRNA丰度随后均下降。低水势阻断了LeEXP8 mRNA积累的初始增加，但未影响LeEXP10，不过LeEXP10 mRNA量在较长时间培养后下降。当种子从脱落酸或低水势溶液转移到水中时，LeEXP8和LeEXP mRNA的丰度均随着萌发而增加。LeEXP8和LeEXP10的组织定位和表达模式表明它们在胚和幼苗生长过程中具有发育阶段特异性作用。
