Abstract
The maize (Zea mays) aleurone layer occupies the single outermost layer of the endosperm. The defective kernel1 (dek1) gene is a central regulator required for aleurone cell fate specification. dek1 mutants have pleiotropic phenotypes including lack of aleurone cells, aborted embryos, carotenoid deficiency, and a soft, floury endosperm deficient in zeins. Here we describe the thick aleurone1 (thk1) mutant that defines a novel negative function in the regulation of aleurone differentiation. Mutants possess multiple layers of aleurone cells as well as aborted embryos. Clonal sectors of thk1 mutant tissue in otherwise normal endosperm showed localized expression of the phenotype with sharp boundaries, indicating a localized cellular function for the gene. Sectors in leaves showed expanded epidermal cell morphology but the mutant epidermis generally remained in a single cell layer. Double mutant analysis indicated that the thk1 mutant is epistatic to dek1 for several aspects of the pleiotropic dek1 phenotype. dek1 mutant endosperm that was mosaic for thk1 mutant sectors showed localized patches of multilayered aleurone. Localized sectors were surrounded by halos of carotenoid pigments and double mutant kernels had restored zein profiles. In sum, loss of thk1 function restored the ability of dek1 mutant endosperm to accumulate carotenoids and zeins and to differentiate aleurone. Therefore the thk1 mutation defines a negative regulator that functions downstream of dek1 in the signaling system that controls aleurone specification and other aspects of endosperm development. The thk1 mutation was found to be caused by a deletion of approximately 2 megabases.
Highlights
The maize (Zea mays) aleurone layer occupies the single outermost layer of the endosperm
The defective kernel1 gene is required for aleurone cell identity, indicating it is required for the response of endosperm cells to peripheral position
In genetic backgrounds that confer anthocyanin pigmentation to the aleurone, recessive thk1 mutant kernels can be recognized on a segregating ear by their dark pigmentation (Fig. 1; Supplemental Fig. S1)
Summary
The maize (Zea mays) aleurone layer occupies the single outermost layer of the endosperm. Barley (Hordeum vulgare) and Aleurone cell fate specification and differentiation has been recently reviewed (Becraft and Yi, 2011) Plants such as cereals that undergo nuclear-type endosperm development show distinct cellular behaviors in the peripheral cell layer compared to internal cells from the onset of cellularization (Brown et al, 1994, 1996, 1999). The peripheral cell layer assumes starchy endosperm cell fate instead of aleurone (Becraft and Asuncion-Crabb, 2000; Becraft et al, 2002; Lid et al, 2002; Wisniewski and Rogowsky, 2004). It appears that SAL1 functions upstream of DEK1 and CR4
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