Regulatory Mechanism of Expression of Stored mRNA Genes in Plant Seeds

通过差异杂交筛选，我们先前从成熟豇豆子叶的总poly（A）^+RNA构建的cDNA文库中选择了一类cDNA克隆（Plant Cell Physiol 31：39-44，1990）。pSAS 10是这一类的克隆，它与吸胀开始（DAI）后1天采集的子叶中poly（A）^+RNA互补的cDNA探针杂交，但不与发育阶段II（开花后13 ~ 15天，DAI）子叶中的cDNA探针杂交。pSAS 10 mRNA仅在发育阶段III（17 - 19 ℃）或更晚的子叶中检测到，并且其水平在种子萌发时开始下降。我们认为pSAS 10 mRNA可能属于“储存”mRNA或在种子成熟后期形成的mRNA，在静止种子中保守，并在萌发早期发挥功能。我们测定了pSAS 10 cDNA的核苷酸序列，包括459 bp和一个约36 bp的poly（A）区，并推导了其产物的氨基酸序列，一个10 kDa的富含半胱氨酸的多肽。pSAS 10 mRNA的合成诱导发芽开始之前，不仅在成熟的种子，而且在未成熟的种子，即使在阶段I（9至11 ℃）和II（13至15 ℃），如果他们被放置在适合发芽的条件。

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.