Stored mRNA in cotyledons of Vigna unguiculata seeds: nucleotide sequence of cloned cDNA for a stored mRNA and induction of its synthesis by precocious germination.

By differential hybridization screening, we previously selected a class of cDNA clones from a lambda gt10 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 probe complementary 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.