Abstract
The aleurone is the outermost layer of cereal endosperm and functions to digest storage products accumulated in starchy endosperm cells as well as to confer important dietary health benefits. Whereas normal maize (Zea mays [Zm]) has a single aleurone layer, naked endosperm (nkd) mutants produce multiple outer cell layers of partially differentiated cells that show sporadic expression of aleurone identity markers such as a viviparous1 promoter-β-glucuronidase transgene. The 15:1 F2 segregation ratio suggested that two recessive genes were involved, and map-based cloning identified two homologous genes in duplicated regions of the genome. The nkd1 and nkd2 genes encode the INDETERMINATE1 domain (IDD) containing transcription factors ZmIDDveg9 and ZmIDD9 on chromosomes 2 and 10, respectively. Independent mutant alleles of nkd1 and nkd2, as well as nkd2-RNA interference lines in which both nkd genes were knocked down, also showed the nkd mutant phenotype, confirming the gene identities. In wild-type kernels, the nkd transcripts were most abundant around 11 to 16 d after pollination. The NKD proteins have putative nuclear localization signals, and green fluorescent protein fusion proteins showed nuclear localization. The mutant phenotype and gene identities suggest that NKD controls a gene regulatory network involved in aleurone cell fate specification and cell differentiation.
Highlights
The aleurone is the outermost layer of cereal endosperm and functions to digest storage products accumulated in starchy endosperm cells as well as to confer important dietary health benefits
We propose that NKD proteins function as transcription factors controlling aleurone layer organization and cell differentiation
We identified the nkd1 and nkd2 genes by map-based cloning as duplicated members of the INDETERMINATE1 domain (IDD) family of zinc finger transcription factors
Summary
The aleurone is the outermost layer of cereal endosperm and functions to digest storage products accumulated in starchy endosperm cells as well as to confer important dietary health benefits. The mutant phenotype and gene identities suggest that NKD controls a gene regulatory network involved in aleurone cell fate specification and cell differentiation. VIVIPAROUS1 (VP1) is a transcription factor containing a B3 domain that binds the CATGCA DNA element to regulate genes that function in seed maturation (Suzuki et al, 1997). The vp gene is required for seed maturation and is the most upstream known transcriptional regulator of the anthocyanin biosynthesis pathway It is expressed in embryo and aleurone cells and is controlled by abscisic acid (ABA; Cao et al, 2007). We propose that NKD proteins function as transcription factors controlling aleurone layer organization and cell differentiation
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