EGY1 plays a role in regulation of endodermal plastid size and number that are involved in ethylene-dependent gravitropism of light-grown Arabidopsis hypocotyls

Abstract

Egy1 was isolated as an ethylene-dependent gravitropism-deficient Arabidopsis mutant. Molecular studies reveal that EGY1 gene encodes a 59-kDa plastid-targeted metalloprotease. It is actively expressed in hypocotyl tissue and targets to endodermal and cortex plastid. Its protein level is up-regulated by both ethylene and light. CAB protein accumulation and chlorophyll level is severely reduced in hypocotyls and endodermal cells, respectively. Sucrose is able to restore the severely reduced starch and lipid contents as well as the deficient endodermal plastid size found in light-grown egy1 hypocotyls yet it fails to rescue the reduced plastid number and chlorophyll level in egy1 endodermal cells. The loss-of-function egy1 mutation results in a smaller size (1.9 +/- 0.3 microm in diameter) and less number (5 +/- 1) of plastids in endodermal cells, which are nearly 50% of the wild-type. EGY1 is specially required for the development of full-size endodermal plastid in seedlings that are grown on sucrose-free media under light. It plays a direct role in controlling the light-induced chlorophyll production, grana formation and plastid replication in endodermal cell. However, it plays an indirect role in regulation of endodermal plastid size. It is likely that the ethylene-dependent gravitropism-deficient phenotype of egy1 hypocotyls may result from the smaller size and less number of endodermal plastids. Gravicurvature assays performed on ethylene-insensitive mutants, etr1-1, etr2-1, ers2-1, ein4-1 and ein2-5, have clearly demonstrated the necessary role for ethylene in vigorous gravitropism of light-grown hypocotyls. The degree of ethylene-dependent gravicurvature is positively correlated with the combined state of endodermal plastid mass and number. Neither ethylene nor EGY1-regulated full-size endodermal plastid is sufficient for promotion of vigorous hypocotyl gravitropism. Presence of 4 full-size plastids per endodermal cell together with ethylene pretreatment of hypocotyls becomes sufficient to trigger vigorous gravicurvature in light-grown seedlings. A model is therefore proposed to address the role of EGY1 in regulation of endodermal plastid size and number as well as the stimulatory effect of ethylene on hypocotyl gravitropism.

Altered Chloroplast Development and Delayed Fruit Ripening Caused by Mutations in a Zinc Metalloprotease at the lutescent2 Locus of Tomato

“…1 and 2). These data are supported by the finding that L2 encodes an ortholog of Arabidopsis EGY1, mutations that disrupt plastid number and development, leading to impaired formation of the thylakoid membranes and reduced accumulation of chlorophyll a/b-binding proteins of the light-harvesting complexes I and II (Chen et al, 2005;Guo et al, 2008). However, a notable difference between l2 and egy1 mutant alleles is that while egy1 mutant alleles have reduced chlorophyll content and are pale throughout development (Chen et al, 2005), leaves of l2 mutants are slow to deetiolate (Fig.…”

Genome-wide association study for soybean cyst nematode resistance in Chinese elite soybean cultivars

“…A homologous gene in Arabidopsis plays a role in the regulation of endodermal plastid size and number. These plasmids are involved in ethylenedependent gravitropism of light-grown hypocotyls (Guo et al 2008). Glyma.13g175200, a GTP-binding related gene, is believed to be associated with resistance genes (R-genes) and regulates the activity of an NADPH oxidase complex in plants (Grant and Loake 2000).…”

Arabidopsis Plastid AMOS1/EGY1 Integrates Abscisic Acid Signaling to Regulate Global Gene Expression Response to Ammonium Stress

“…It is required for normal chloroplast development, including the formation of thylakoid grana, the lamella system, and the accumulation of chlorophyll and chlorophyll a/b-binding proteins in chloroplast membranes. Additionally, EGY1 is required for ethylene-dependent gravitropism of light-grown hypocotyls, a process linked to the regulation of endodermal plastid size and number (Chen et al, 2005;Guo et al, 2008). Our work furthermore explores the role of abscisic acid (ABA) signaling as a downstream component of an AMOS1/ EGY1-dependent plastid retrograde signaling pathway, in the context of regulation of the gene expression and protection of chloroplast functionalities from NH 4 + stress.…”