sal1 determines the number of aleurone cell layers in maize endosperm and encodes a class E vacuolar sorting protein

Abstract

A microscopy-based screen of a large collection of maize Mutator (Mu) transposon lines identified the supernumerary aleurone layers 1-1 (sal1-1) mutant line carrying up to seven layers of aleurone cells in defective kernel endosperm compared with only a single layer in wild-type grains. Normal, well filled endosperm that is homozygous for the sal1-1 mutant allele contains two to three layers of aleurone cells. Cloning of the sal1 gene was accomplished by using Mu tagging, and the identity of the cloned gene was confirmed by isolating an independent sal1-2 allele by reverse genetics. Homozygous sal1-2 endosperm has two to three layers of aleurone cells in normal, well filled grains. In situ hybridization experiments reveal that the sal1 gene is ubiquitously expressed in vegetative as well as zygotic grain tissues, with no difference being detected between aleurone cells and starchy endosperm cells. Northern blot analysis failed to detect the sal1-2 transcript in leaves of homozygous plants, suggesting that the allele is a true sal1 knockout allele. The sal1 gene encodes a homologue of the human Chmp1 gene, a member of the conserved family of the class E vacuolar protein sorting genes implicated in membrane vesicle trafficking. In mammals, CHMP1 functions in the pathway targeting plasma membrane receptors and ligands to lysosomes for proteolytic degradation. Possible roles for the function of the sal1 gene in aleurone signaling, including a defect in endosome trafficking, are discussed.

Exploring the ESCRTing machinery in eukaryotes

“…MVBs might also be involved in recycling membranes. Although the presence of MVBs and their roles as prevacuolar compartments for lytic and storage vacuoles, in vacuolar receptor recycling, and in internalization and secretion of arabinogalactan-rich glycoproteins have been described [2,4,5,[13][14][15][16]18], only a few reports have identified components of the ESCRT-machinery in plants [53,54,67]. Here we show by cross-species comparisons that most protein entry components and all the ESCRT-components are present in Arabidopsis and rice.…”

“…However, two other SNF7 domain proteins, VPS46 or CHMP1 and VPS60 or CHMP5, have been identified in the yeast or mammalian genomes, respectively, and also in our analyses of plants, Drosophila and C. elegans. A CHMP1 homolog has been identified in maize by using a genetic approach to identify regulators that determine the number of aleurone layers [53]. Whereas the homozygous sal1 mutants of maize do not germinate, the depletion of the Nicotiana benthamiana CHMP1 homolog NbCHMP1 resulted in only subtle changes in leaf morphology and color [54].…”

Surface Position, Not Signaling from Surrounding Maternal Tissues, Specifies Aleurone Epidermal Cell Fate in Maize

“…Homozygous dek1 endosperms almost entirely lack aleurone cells, and embryos are arrested at the globular stage of development (Lid et al, 2002). The third gene, sal1, encodes a 204-amino acid protein that is homologous to the human charged vesicular body protein 1/Chromatin modulating protein 1 (Chmp1) protein, a member of the conserved family of E-class vacuolar sorting proteins (Shen et al, 2003). Homozygous sal1 endosperms have multiple layers of aleurone cells, suggesting a role for Sal1 in inhibiting aleurone cell fate specification (Shen et al, 2003).…”

“…The third gene, sal1, encodes a 204-amino acid protein that is homologous to the human charged vesicular body protein 1/Chromatin modulating protein 1 (Chmp1) protein, a member of the conserved family of E-class vacuolar sorting proteins (Shen et al, 2003). Homozygous sal1 endosperms have multiple layers of aleurone cells, suggesting a role for Sal1 in inhibiting aleurone cell fate specification (Shen et al, 2003). Exactly how these three proteins operate in a signaling cascade leading to endosperm cell differentiation remains unknown.…”

Between the sheets: inter–cell–layer communication in plant development

“…Whether CR4 is a direct target of DEK1, or whether DEK1 could cleave the precursor of a CR4 ligand, remains to be shown (Lid et al 2002;Becraft et al 2002). A further potential element in this signalling pathway, the SUPERNUMERARY ALEURONE LAY-ERS1 (SAL1) gene has recently been described (Shen et al 2003). SAL1 encodes a class E vacuolar sorting protein similar to proteins, which, in animal systems, have been implicated in the turnover of plasma-membrane receptors.…”