Subcellular localization of rice acyl‐CoA‐binding proteins (ACBPs) indicates that OsACBP6::GFP is targeted to the peroxisomes

Abstract

Summary Acyl‐CoA‐binding proteins (ACBPs) show conservation at the acyl‐CoA‐binding (ACB) domain which facilitates binding to acyl‐CoA esters. In Arabidopsis thaliana, six ACBPs participate in development and stress responses. Rice (Oryza sativa) also contains six genes encoding ACBPs. We investigated differences in subcellular localization between monocot rice and eudicot A. thaliana ACBPs. The subcellular localization of the six OsACBPs was achieved via transient expression of green fluorescence protein (GFP) fusions in tobacco (Nicotiana tabacum) epidermal cells, and stable transformation of A. thaliana. As plant ACBPs had not been reported in the peroxisomes, OsACBP6::GFP localization was confirmed by transient expression in rice sheath cells. The function of OsACBP6 was investigated by overexpressing 35S::OsACBP6 in the peroxisomal abc transporter1 (pxa1) mutant defective in peroxisomal fatty acid β‐oxidation. As predicted, OsACBP1::GFP and OsACBP2::GFP were localized to the cytosol, and OsACBP4::GFP and OsACBP5::GFP to the endoplasmic reticulum (ER). However, OsACBP3::GFP displayed subcellular multi‐localization while OsACBP6::GFP was localized to the peroxisomes. 35S::OsACBP6‐OE/pxa1 lines showed recovery in indole‐3‐butyric acid (IBA) peroxisomal β‐oxidation, wound‐induced VEGETATIVE STORAGE PROTEIN1 (VSP1) expression and jasmonic acid (JA) accumulation. These findings indicate a role for OsACBP6 in peroxisomal β‐oxidation, and suggest that rice ACBPs are involved in lipid degradation in addition to lipid biosynthesis.

Rice acyl-CoA-binding proteins OsACBP4 and OsACBP5 are differentially localized in the endoplasmic reticulum of transgenicArabidopsis

“…19 With the exception of the cytosolic localization of class I ACBPs, the remaining classes demonstrate differential localization between rice and Arabidopsis. 19 Both Arabidopsis and rice class II and class III members have been predicted by computational analysis to be targeted to the endomembranes; however, experimental verification has proven otherwise. 19 Although OsACBP4 and OsACBP5 are not phylogenetically grouped in the same class, they are confined to the ER.…”

“…19 In 35S::OsACBP4::GFPtransformed Arabidopsis, OsACBP4::GFP fluorescence was located close to the nuclear envelope in many root cells ( Fig. 2A), in contrast to the clear edge of the nuclear envelope for OsACBP5::GFP (Fig.…”

“…It has been reported that some ACBPs show uniqueness in their affinity for lipid substrates. 2,19 Although the specific functions of OsACBPs are not fully understood, their induced expression by various stresses, such as drought, high salinity, wounding, and pathogen infection, suggests that they are involved in stress responses. Although OsACBP4 and OsACBP5 belong to different classes of the ACBP family, they are both subcellularly localized to the ER.…”

“…Although OsACBP4 and OsACBP5 belong to different classes of the ACBP family, they are both subcellularly localized to the ER. 3,19 OsACBP4 contains C-terminal ankyrin repeats, falling into class II and resembling AtACBP1 and AtACBP2, while OsACBP5 is a large ACBP similar to AtACBP3 and belongs to class III. 3 Our recent findings have shown that the localization of OsACBP4 and OsACBP5 overlapped at the peripheral tubular ER (but not cisternal ER) in transgenic Arabidopsis.…”

“…3 Our recent findings have shown that the localization of OsACBP4 and OsACBP5 overlapped at the peripheral tubular ER (but not cisternal ER) in transgenic Arabidopsis. 19 The ER is a network composed of several domains, including the nuclear envelope, the central cisternal ER (cec ER), and the peripheral tubular and cisternal ER. 20 Species-specific ER-derived structures that are known include ER bodies from the order Brassicales and protein bodies from maize and rice.…”