The Arabidopsis Cytosolic Acyl-CoA-Binding Proteins Play Combinatory Roles in Pollen Development

Abstract

In Arabidopsis, six acyl-CoA-binding proteins (ACBPs) have been identified and they have been demonstrated to function in plant stress responses and development. Three of these AtACBPs (AtACBP4-AtACBP6) are cytosolic proteins and all are expressed in floral organs as well as in other tissues. The roles of cytosolic AtACBPs in floral development were addressed in this study. To this end, a T-DNA insertional knockout mutant of acbp5 was characterized before use in crosses with the already available acbp4 and acbp6 T-DNA knockout mutants to examine their independent and combinatory functions in floral development. The single-gene knockout mutations did not cause any significant phenotypic changes, while phenotypic deficiencies affecting siliques and pollen were observed in the double mutants (acbp4acbp6 and acbp5acbp6) and the acbp4acbp5acbp6 triple mutant. Vacuole accumulation in the acbp4acbp6, acbp5acbp6 and acbp4acbp5acbp6 pollen was the most severe abnormality occurring in the double and triple mutants. Furthermore, scanning electron microscopy and transmission electron microscopy revealed exine and oil body defects in the acbp4acbp5acbp6 mutant, which also displayed reduced ability in in vitro pollen germination. Transgenic Arabidopsis expressing β-glucuronidase (GUS) driven from the various AtACBP promoters indicated that AtACBP6pro::GUS expression overlapped with AtACBP4pro::GUS expression in pollen grains and with AtACBP5pro::GUS expression in the microspores and tapetal cells. Taken together, these results suggest that the three cytosolic AtACBPs play combinatory roles in acyl-lipid metabolism during pollen development.

Plant acyl-CoA-binding proteins: An emerging family involved in plant development and stress responses

“…Subsequent GUS assays revealed the expression of AtACBP4 in pollen grains, AtACBP5 in microspores and tapetal cells, and AtACBP6 in pollen grains, microspores and tapetal cells, suggesting their overlapping roles in pollen development [122]. In addition, AtACBP6 was also expressed in the cotyledons, hypocotyl and cotyledonary-staged embryo in GUS-histochemical assays [32].…”

“…2) [28]. Recent expression profiles by quantitative RT-PCR showed that AtACBP4 to AtACBP6 were highly expressed in the inflorescences [122].…”

Acyl-CoA-Binding Protein ACBP1 Modulates Sterol Synthesis during Embryogenesis

“…For histochemical examination, the specimens were embedded and sectioned in Technovit 7100 (Electron Microscopy Sciences). Sections were stained with the periodic acid-Schiff's reaction for total insoluble carbohydrates and Amido Black 10B for protein and then imaged with a Leitz photomicroscope using a Nikon DS-Fi2 digital camera according to Hsiao et al (2015).…”

Transport and transcriptional regulation of oil production in plants

“…Mutant acbp4/5/6 pollen grains exhibit defects in oil bodies and the outer pollen cell wall. [50] Hence, LACS and ACBPs work in a combination to export the lipid precursors for cell wall deposition.…”