The Putative E3 Ubiquitin Ligase ECERIFERUM9 Regulates Abscisic Acid Biosynthesis and Response during Seed Germination and Postgermination Growth in Arabidopsis    

Abstract

The ECERIFERUM9 (CER9) gene encodes a putative E3 ubiquitin ligase that functions in cuticle biosynthesis and the maintenance of plant water status. Here, we found that CER9 is also involved in abscisic acid (ABA) signaling in seeds and young seedlings of Arabidopsis (Arabidopsis thaliana). The germinated embryos of the mutants exhibited enhanced sensitivity to ABA during the transition from reversible dormancy to determinate seedling growth. Expression of the CER9 gene is closely related to ABA levels and displays a similar pattern to that of ABSCISIC ACID-INSENSITIVE5 (ABI5), which encodes a positive regulator of ABA responses in seeds. cer9 mutant seeds exhibited delayed germination that is independent of seed coat permeability. Quantitative proteomic analyses showed that cer9 seeds had a protein profile similar to that of the wild type treated with ABA. Transcriptomics analyses revealed that genes involved in ABA biosynthesis or signaling pathways were differentially regulated in cer9 seeds. Consistent with this, high levels of ABA were detected in dry seeds of cer9. Blocking ABA biosynthesis by fluridone treatment or by combining an ABA-deficient mutation with cer9 attenuated the phenotypes of cer9. Whereas introduction of the abi1-1, abi3-1, or abi4-103 mutation could completely eliminate the ABA hypersensitivity of cer9, introduction of abi5 resulted only in partial suppression. These results indicate that CER9 is a novel negative regulator of ABA biosynthesis and the ABA signaling pathway during seed germination.

Insights into endoplasmic reticulum‐associated degradation in plants

“…CER9/DOA10A/SUD1 was identified as a negative regulator of the abscisic acid (ABA) response in seed germination and early seedling growth, which is consistent with the drought-tolerant phenotype of cer9/doa10a/sud1, which exhibits sensitivity to ABAinduced stomatal closure (Zhao et al, 2014). A defect in CER9/ DOA10A/SUD1 also revealed an increased degree of dormancy, which can be detected via increased ABA levels in cer9/doa10a/sud1 dry seeds (Zhao et al, 2014). However, target proteins of DOA10A in ABA and drought signalling were not explored in these studies, nor was the E3 ligase activity of DOA10A demonstrated (Doblas et al, 2013;Zhao et al, 2014).…”

“…In a study by Doblas et al (), ECERIFERUM 9 ( CER9 ), also named DOA10A and SUPPRESSOR OF DRY2 DEFECTS1 ( SUD1 ), an important ubiquitin E3 ligase in ERAD, was obtained by screening the suppressor of dry2 ( drought hypersensitive2 ), and the defect in CER9/DOA10A/SUD1 exhibited increased tolerance to drought stress. CER9/DOA10A/SUD1 was identified as a negative regulator of the abscisic acid (ABA) response in seed germination and early seedling growth, which is consistent with the drought‐tolerant phenotype of cer9/doa10a/sud1 , which exhibits sensitivity to ABA‐induced stomatal closure (Zhao et al , ). A defect in CER9/DOA10A/SUD1 also revealed an increased degree of dormancy, which can be detected via increased ABA levels in cer9/doa10a/sud1 dry seeds (Zhao et al , ).…”

From start to finish: amino‐terminal protein modifications as degradation signals in plants

“…A functional Ac/N‐end rule pathway has not yet been identified in plants, although NATs, and proteins with high sequence similarity to both DOA10 and NOT4, exist in Arabidopsis (Gibbs et al ., ; Gibbs, ). Interestingly, mutants of the Arabidopsis DOA10‐like gene ECERIFERUM9/SUPPRESSOR OF DRY2 DEFECTS1 ( CER9/SUD1 ) display ABA‐hypersensitivity during seed germination, similar to the ABA‐associated phenotypes observed in NATA‐deficient plants (Zhao et al ., ; Linster et al ., ). If Nt‐acetylation acts as a degradation signal, accumulation of its substrates would be expected in both the natA and cer9 / sud1 mutants; it is therefore possible that proteins associated with ABA signalling might be targets of a plant Ac/N‐end rule pathway.…”

Medicago falcata MfSTMIR, an E3 ligase of endoplasmic reticulum‐associated degradation, is involved in salt stress response

“…Some of these E3 ubiquitin ligases participate in abiotic stress response. CER9 is a negative regulator of cuticle lipid synthesis and ABA biosynthesis, whose deficiency increases cuticle lipid deposition and improves plant tolerance to water deficit (Lu et al ., ; Zhao et al ., ). Rma1H1 is involved in the degradation of the aquaporin isoform PIP2;1 to regulate its plasma membrane level.…”