Regulatory Mechanism of Expression of Stored mRNA Genes in Plant Seeds

通过差异杂交筛选，我们先前从成熟的豌豆子叶总Poly(A)^+RNA构建的lambdagt10 cDNA文库中筛选出了一类克隆。PSAS10是这一类的一个克隆，它与吸胀开始后1天(DAI)收集的子叶中的Poly(A)~+RNA的cDNA探针杂交，但不与发育阶段II(开花后13~15天，DAF)的子叶的cDNA探针杂交。PSAS10基因只有在发育III期(17~19天)或以后的子叶中检测到，当种子萌发时，pSAS10基因的表达水平开始下降。我们认为，pSAS10可能属于‘储存’类，或在种子成熟后期形成的，在静止的种子中保守，在萌发早期发挥功能的mRNA。我们测定了pSAS10基因的核苷酸序列，全长459个核苷酸和一个约36个核苷酸的聚(A)区，并推导出其产物的氨基酸序列，即一个10 kDa的富含半胱氨酸的多肽。在适宜的萌发条件下，pSAS10mRNA的合成不仅在成熟种子中被诱导，而且在I期(9~11天)和II期(13~15天)的未成熟种子中也是如此。

By differential hybridization screening, we previously selected a class of cDNA clones from a lambdagt10 cDNA library that was constructed from the total poly (A) ^+RNA of mature cowpea cotyledons (Plant Cell Physiol 31 : 39-44, 1990). pSAS10, a clone of this class, hybridized with a cDNA probecomplementary to poly (A) ^+RNA from cotyledons collected 1 day after the onset of imbibition (DAI), but not with the cDNA probe from cotyledons at developmental stage II (13 to 15 days after flowering, DAF). pSAS10 mRNA was detectable only in cotyledons at developmental stage III (17 to 19 DAF) or later, and its level began to decline when seeds germinated. We have suggested that pSAS10 mRNA is likely to belong to the class of 'stored' mRNA or the mRNA that is formed at the late stage of seed maturation, is conserved in quiescent seeds and becomes functional at the early stage of germination. We determined the nucleotide sequence of pSAS10 cDNA consisting of 459 bp and an approximately 36 bp poly(A) tract, and deduced the amino acid sequence of its product, a 10-kDa cysteine-rich polypeptide. Synthesis of pSAS10 mRNA was induced just before germination began, not only in mature seeds but also in immature seeds even at stages I (9 to 11 DAF) and II (13 to 15 DAF) if they were placed under conditions suitable for germination.