Regulatory Mechanism of Expression of Stored mRNA Genes in Plant Seeds

通过差异杂交筛选，我们从成熟豇豆子叶总poly (a) ^+RNA构建的lambdagt10 cDNA文库中筛选出一类cDNA克隆（Plant Cell Physiol 31: 39-44, 1990）。该属无性系pSAS10与吸吸后1天采集的子叶中poly (a) ^+RNA的cDNA探针进行杂交，但未与发育第II期（开花后13 ~ 15天）子叶中的cDNA探针进行杂交。pSAS10 mRNA仅在发育第III期（17 ~ 19 DAF）或更晚的子叶中检测到，其水平在种子萌发时开始下降。我们认为pSAS10 mRNA可能属于“储存”mRNA的类别，或者是在种子成熟后期形成的mRNA，在静止种子中保存，并在萌发早期开始发挥功能。我们测定了pSAS10 cDNA的459 bp和约36 bp的聚(A)区核苷酸序列，并推导出其产物10-kDa的富含半胱氨酸的多肽的氨基酸序列。pSAS10 mRNA的合成在萌发开始前被诱导，不仅在成熟种子中，而且在I期（9 - 11 DAF）和II期（13 - 15 DAF）的未成熟种子中也被诱导，如果它们被置于适合发芽的条件下。

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.