Minisymposium 13: Seed Biology

Abs # 25001: superal1 determines the number of aleurone cell layers in maize endosperm and encodes a CHMP family member of the class E vacuolar sorting proteins

Presenter:	Shen, Bo , bo.shen@pioneer.com
Authors	Shen, Bo  (A)   Li, Changjiang  (A)   Min, Zhao  (A)   Meeley, Robert  (A)   Tarczynski, Mitchell  (A)   Olsen, Odd-Arne  (A)
Affiliations:	(A): Pioneer Hi-Bred International, A DuPont Company

Aleurone cell contains oil, high quality protein, and phytosterols, and plays an important role during seed germination. A microscopy based screen of a large collection of Pioneer Mutator-transposon lines identified the superal1-1 (sal1-1) mutant line carrying up to seven layers of aleurone cells in defective kernel endosperm, compared to only a single layer in wild-type grains. Superal1 gene was cloned 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. Expression analysis reveals that the superal1 gene is ubiquitously expressed in vegetative as well as in 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 Superal1 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. In contrast to multi-aleurone layers in superal 1, maize mutants, crinkly 4 and defective kernel 1 (dek1), lack aleurone cells partially or completely. Crinkly 4 was cloned previously by Philip Becraft and encodes a membrane receptor kinase. Dek1 encodes a plant homologue of animal calpain. DEK1 protein contains 21 transmembrane domains, an extra-cellular loop domain, and an intra-cellular cysteine proteinase domain. We demonstrated that over-expression of Crinkly 4 receptor resulted in two layers of aleurone cells in transgenic maize plant, indicating that Crinkly 4 by itself is sufficient to determine aleurone cell fate. The potential role of vesicle trafficking in controlling receptor turnover and aleurone cell formation will be discussed.