Allelic variation and differential expression of methionine-rich δ-zeins in maize inbred lines B73 and W23a1

Abstract

The sulfur-amino-acid-rich δ-zeins of maize (Zea mays L.) are represented by 18-kDa and 10-kDa proteins. We have cloned a novel 11-kDa methionine-rich δ-zein from developing endosperm of the inbred line W23a1. The nucleotide sequence of this new δ-zein is identical to the published 10-kDa δ-zein, except for an insertion of 18 nucleotides between +316 and +333 bp from the translation start site. Antibodies raised against the recombinant 18-kDa δ-zein recognized both the 18-kDa and 10-kDa δ-zein from total seed protein extracts of different maize inbred lines. Western blot analysis revealed differences in the levels of the δ-zeins in different inbred lines and some of the inbred lines lacked either the 10-kDa or the 18-kDa δ-zeins. Northern blot analysis revealed temporal differences in the RNA transcript levels of the 11-kDa and 18-kDa δ-zeins between B73 and W23a1. Such differences were not evident on Western blot analysis where similar protein accumulation profiles were seen for both lines. Immunostaining of paraffin sections of developing maize endosperm with the 18-kDa δ-zein antibodies revealed specific labeling of protein bodies found in the first few starchy layers from the aleurone layer. Electron-microscopic observation of thin-sections of B73 and W23a1 endosperm cells confirmed the presence of recently discovered novel, vacuole-like structures in these inbred lines. Immunogold labeling studies revealed that the δ-zeins were localized in the endoplasmic-reticulum-derived protein bodies and showed no preferential gold particle labeling over either the light or electron-dense material found in these protein bodies.