HOS3, an ELO-Like Gene, Inhibits Effects of ABA and Implicates a S-1-P/Ceramide Control System for Abiotic Stress Responses in Arabidopsis thaliana

Abstract

A hyper-osmotically sensitive mutant of Arabidopsis thaliana, designated hos3-1 (high expression of osmotically responsive genes), was identified based on its hyper-luminescence of RD29A:LUC promoter fusion plants upon treatment with NaCl and ABA. These responses implicate the disrupted gene as a direct or indirect negative regulator of the RD29A stress-responsive pathway. By sequencing the flanking regions of the T-DNA borders, it was determined that the disrupted gene is at locus At4g36830, annotated as encoding a putative protein with high homology to CIG30 (ELO2/FEN1). CIG30 has been implicated in synthesis of very long chain fatty acids (VLCFA), which are essential precursors for sphingolipids and ceramides. Altered stress responses characteristic of ABA-hypersensitivity, including reduced root growth inhibition and reduced germination with ABA treatment and reduced water loss from leaves, were exhibited by allelic hos3-1 and hos3-2 mutants. The hos3-2 mutant is partially suppressed in its transcript abundance and is inherited as a recessive trait. Further, the HOS3 ORF under the control of the 35SCaMV promoter restored wild-type NaCl- and ABA-root growth sensitivity as well as RD29A:LUC luminescence in mutant plants. We also show here that the HOS3 wild-type gene functionally complements the sensitivity of elo2 and elo3 yeast mutants to monensin. Furthermore, both hos3-1 and hos3-2 alleles shared increased sensitivity to the herbicide Metolachlor, which inhibits acyl chain elongation in synthesis of VLCFA, and HOS3 functionally complemented both elo2 and elo3 and restored levels of VLCFA. Together, these data establish that HOS3 inhibits ABA-mediated stress responses and implicate the VLCFA pathway and products as control points for several aspects of abiotic stress signaling and responses. The results also provide support for a role of ceramide in the control of stomatal behavior.

Apoplastic Diffusion Barriers in Arabidopsis

“…Disruption of VLCFA production in the hos3 mutant causes ceramide deficiency and affects ABA-related stress responses, such as root growth inhibition, seed germination with ABA treatment and water loss from leaves. These results implicate HOS3 and VLCFA pathway products in several aspects of ABAmediated stress signaling (Quist et al, 2009).…”

ECERIFERUM2-LIKE Proteins Have Unique Biochemical and Physiological Functions in Very-Long-Chain Fatty Acid Elongation

“…There are two families of condensing enzymes in Arabidopsis (Arabidopsis thaliana). The ELONGATION-DEFECTIVE (ELO)-LIKE family is homologous to yeast (Saccharomyces cerevisiae) ELOs, and has putative functions in sphingolipid biosynthesis (Quist et al, 2009). Although our current understanding of plant ELO-LIKE physiological function and biochemical activity is limited, the mechanism of yeast Elo protein activity has been thoroughly investigated (Denic and Weissman, 2007).…”

Functional identification of ELO-like genes involved in very long chain fatty acid synthesis in Arabidopsis thaliana

“…However, we found that AtELO4 exhibited predominantly high expression in roots and weaker expression in leaves. In addition, previous studies showed that loss of function mutants of AtELO4 resulted in decreased VLCFA in roots and affected root growth [8], suggesting that AtELO4 played an important role in roots. Therefore, more complete and accurate temporal and spatial expres sion data for AtELO family was presented in our study.…”

“…ELO [7]. AtELO4, one member of ELO like family was confirmed to comple ment yeast ELO2 and ELO3 mutants and reduced the expression of AtELO4 resulted in approximately 15% increase in C22:0 level, 20% increase in C24:0 level, and 35% decrease in C26:0 level in leaves of atelo4 mutants as compared with those in Arabidopsis wild type plants [8]. However, much information of ELO like family members on developmental expres sion pattern, subcellular localization, and fatty acid profiles in AtELO knock out/down mutants remains elusive.…”

“…Considering the fact that AtELO2 was barely detected in any examined tis sues and AtELO4 had been reported to function as a considering enzyme involved in VLCFA synthesis in Arabidopsis [8], two salk lines, salk_090523c (atelo1) and salk_108023c (atelo3), obtained from the Arabi dopsis Biological Resource Center, were found to carry T DNA insertions in the second exon of AtELO1 and the end of exon of AtELO3, respectively (Fig. 3).…”