Opaque1 Encodes a Myosin XI Motor Protein That Is Required for Endoplasmic Reticulum Motility and Protein Body Formation in Maize Endosperm

Abstract

Myosins are encoded by multigene families and are involved in many basic biological processes. However, their functions in plants remain poorly understood. Here, we report the functional characterization of maize (Zea mays) opaque1 (o1), which encodes a myosin XI protein. o1 is a classic maize seed mutant with an opaque endosperm phenotype but a normal zein protein content. Compared with the wild type, o1 endosperm cells display dilated endoplasmic reticulum (ER) structures and an increased number of smaller, misshapen protein bodies. The O1 gene was isolated by map-based cloning and was shown to encode a member of the plant myosin XI family (myosin XI-I). In endosperm cells, the O1 protein is associated with rough ER and protein bodies. Overexpression of the O1 tail domain (the C-terminal 644 amino acids) significantly inhibited ER streaming in tobacco (Nicotiana benthamiana) cells. Yeast two-hybrid analysis suggested an association between O1 and the ER through a heat shock protein 70-interacting protein. In summary, this study indicated that O1 influences protein body biogenesis by affecting ER morphology and motility, ultimately affecting endosperm texture.

Identification and Characterization of Maizefloury4as a Novel Semidominant Opaque Mutant That Disrupts Protein Body Assembly

“…Four genes corresponding to recessive mutants, opaque1 (o1), o2, o5, and o7, have been cloned (Schmidt et al, 1990;Miclaus et al, 2011;Myers et al, 2011;Wang et al, 2011Wang et al, , 2012, the majority of which result from defects in storage protein synthesis, which affects endosperm texture. For example, O2 encodes a transcriptional factor that positively regulates the expression level of 22-kD a-zeins (Damerval and Devienne, 1993).…”

Nonredundant Function of Zeins and Their Correct Stoichiometric Ratio Drive Protein Body Formation in Maize Endosperm

“…QPM has low levels of a-zeins, like o2, but the 27-kD g-zein is increased 2-to 3-fold (Wallace et al, 1990;Geetha et al, 1991;Lopes and Larkins, 1991;Holding et al, 2011); the degree of endosperm vitreousness closely correlates with the level of 27-kD g-zein protein , and this increase causes the observed elevation in protein body number in QPM Moro et al, 1995) consistent with the proposed role of 27-kD g-zein in protein body initiation. Some other opaque mutants are the result of aberrations in processes unrelated to protein bodies, such as amino acid biosynthesis, plastid development, and cytoskeletal function Myers et al, 2011;Wang et al, 2012). This indicates that further work is needed to generate a more complete understanding of the factors that control endosperm maturation.…”

Deletion Mutagenesis Identifies a Haploinsufficient Role for γ-Zein in opaque2 Endosperm Modification

“…Furthermore, the possible role of the 50-kD g-zein in modification has not been previously addressed. The molecular characterization of opaque mutants has shown that vitreous endosperm formation depends on more than just correct abundance and spatial organization of zein proteins (Holding and Larkins, 2006;Holding et al, 2007Holding et al, , 2010Myers et al, 2011;Wang et al, 2012). Furthermore, mapping studies indicate there are several QTLs for endosperm modification in QPM Holding et al, 2008Holding et al, , 2011.…”