Arabidopsis acyl-CoA-binding protein ACBP6 localizes in the phloem and affects jasmonate composition

Abstract

Arabidopsis thaliana ACYL-COA-BINDING PROTEIN6 (AtACBP6) encodes a cytosolic 10-kDa AtACBP. It confers freezing tolerance in transgenic Arabidopsis, possibly by its interaction with lipids as indicated by the binding of acyl-CoA esters and phosphatidylcholine to recombinant AtACBP6. Herein, transgenic Arabidopsis transformed with an AtACBP6 promoter-driven β-glucuronidase (GUS) construct exhibited strong GUS activity in the vascular tissues. Immunoelectron microscopy using anti-AtACBP6 antibodies showed AtACBP6 localization in the phloem especially in the companion cells and sieve elements. Also, the presence of gold grains in the plasmodesmata indicated its potential role in systemic trafficking. The AtACBP6 protein, but not its mRNA, was found in phloem exudate of wild-type Arabidopsis. Fatty acid profiling using gas chromatography-mass spectrometry revealed an increase in the jasmonic acid (JA) precursor, 12-oxo-cis,cis-10,15-phytodienoic acid (cis-OPDA), and a reduction in JA and/or its derivatives in acbp6 phloem exudates in comparison to the wild type. Quantitative real-time PCR showed down-regulation of COMATOSE (CTS) in acbp6 rosettes suggesting that AtACBP6 affects CTS function. AtACBP6 appeared to affect the content of JA and/or its derivatives in the sieve tubes, which is consistent with its role in pathogen-defense and in its wound-inducibility of AtACBP6pro::GUS. Taken together, our results suggest the involvement of AtACBP6 in JA-biosynthesis in Arabidopsis phloem tissues.

Arabidopsis acyl‐CoA‐binding proteins regulate the synthesis of lipid signals

“…The downregulation of CTS in atacbp6 rosettes implicates that AtACBP6 may facilitate CTS‐mediated OPDA transport, although the binding of AtACBP6 with OPDA‐CoA has not been verified (Ye et al ., ). While jasmonate synthesis is inducible by wound signals from a distal site (Dave & Graham, ; Wasternack & Feussner, ), AtACBP6 promoter activity was also upregulated systemically by wounding (Ye et al ., ), corroborating the tight correlation of AtACBP6 and oxylipin signaling. The role of AtACBP3 in the jasmonate‐mediated defense response has been better substantiated (Hu et al ., ).…”

“…COMATOSE (CTS) transports OPDA in its free acid or CoAactivated form into the peroxisome (Schaller et al, 2008), where it is reduced and converted into jasmonates via three rounds of boxidation (Dave & Graham, 2012). AtACBP3 and AtACBP6 are linked to jasmonate synthesis (Ye et al, 2016;Hu et al, 2018). Ye et al (2016) demonstrated that the phloem exudates of atacbp6 contained lower linoleic acid, linolenic acid and jasmonates but higher cis-OPDA.…”

“…The phloem exudates of atacbp3 and AtACBP3-RNAi contained lower methyl jasmonate and precursor FAs, and micrografting indicated that AtACBP3 is phloem-mobile . Thus, it appears that cytosolic AtACBP6 and extracellularly localized AtACBP3 cooperate to regulate jasmonate synthesis by influencing FA and oxylipin composition in the phloem via symplastic and apoplastic transport, respectively (Ye et al, 2016;Hu et al, 2018).…”

Plasmodesmal regulation during plant–pathogen interactions

“…Supporting a model of dependence of defence hormone signalling on symplast regulation, plants that overexpress PDLP5 (and consequently have reduced PD SEL) also have reduced JA in petiole exudates, suggesting reduced symplastic access to the phloem (Lim et al ., ), and the PDLP triple mutant pdlp1,2,3 exhibits mis‐regulation of JA‐dependent gene expression and reduced accumulation of JA in the context of herbivory (Bricchi et al ., ). Further, ACYL‐COA‐BINDING PROTEIN 6 (AtCBP6), which is proposed to regulate the cytosolic acyl‐CoA ester pool and JA production, is symplastically mobile within the phloem (Ye et al ., ).…”

“…Further, ACYL-COA-BINDING PROTEIN 6 (AtCBP6), which is proposed to regulate the cytosolic acyl-CoA ester pool and JA production, is symplastically mobile within the phloem (Ye et al, 2016).…”