Osmolyte-related recovery of the opaque-6 lethal phenotype in Zea mays L


Endosperm growth and development is a complex phenomenon, driven by the coordinate expression of several genes. A series of endosperm mutants with altered timing and zein synthesis rate have been studied, allowing the partial unravelling of a multifarious system, integrating carbohydrate, amino acid, and storage protein me¬tabolisms, and operating during endosperm growth and development. The exact biological function of one of these loci, the Opaque-6 (O6) gene, remains to be acknowledged. The o6 locus determines a general reduction of 19- and 22 kDa zeins as well as a number of non-zein polypeptides present in the wild type endosperm. The o6 mutants present a collapsed, dull endosperm, leaf striations and early seedling death; however, o6 seedlings can survive when grown in the presence of exogenous proline. It has been suggested that, in mutant seeds and in con¬trast with the development of the normal seeds, proline does not reach the sites of protein synthesis in adequate amounts. Yet, it has been demonstrated that amino acids other than proline are also able to restore o6 seedling le¬thality, contradicting this hypothesis. In this paper, we explored the possibility that the observed proline-mediated rescue of o6 mutant seedling lethality regarded an osmolyte-mediated mitigation of aberrant protein folding rather than the restoration of a reduced proline flux needed for protein synthesis. This hypothesis was tested by means of in vitro cultivation of o6 seedlings in the presence of putative osmolytes including a series of amino acids, me¬thylamines, and polyols. Several osmolytes were identified, which were able to restore normal growth in o6 mutant seedlings. Root reestablishment required higher osmolyte concentrations than those necessary for the recovery of the aboveground plant parts. The results presented in this paper provide sufficient preliminary evidence to assume that proline-induced recovery of the o6 mutant phenotype depends on the osmolytic properties of this amino acid.


Zea mays; opaque-6; seedling lethality; osmolytes

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