Barley has two peroxisomal ABC transporters with multiple functions in β-oxidation

Area of Science:

• Plant Biology
• Molecular Biology
• Biochemistry

Background:

• Peroxisomal beta-oxidation is crucial for lipid breakdown, jasmonate synthesis, and auxin metabolism in plants.
• Subfamily D ATP-binding cassette (ABC) transporters import substrates into peroxisomes, with Arabidopsis COMATOSE (CTS) being essential.
• Barley, a cereal crop, stores starch and possesses two CTS homologues, HvABCD1 and HvABCD2.

Purpose of the Study:

• Investigate the roles of peroxisomal ABCD transporters (HvABCD1 and HvABCD2) in barley.
• Determine their functions in substrate metabolism, jasmonate biosynthesis, and grain development.
• Compare conserved functions with oilseed plants.

Main Methods:

• Utilized RNA interference (RNAi) to suppress HvABCD1 and HvABCD2 in barley.
• Transformed the Arabidopsis cts-1 null mutant with barley homologues.
• Assessed complementation of phenotypes including germination, hypocotyl sensitivity, and seed size.
• Tested HvABCD1 in a yeast pxa1/pxa2Δ mutant for fatty acid beta-oxidation.

Main Results:

• HvABCD1 and HvABCD2 are involved in 2,4-dichlorophenoxybutyrate (2,4-DB) and indole butyric acid (IBA) metabolism, jasmonate biosynthesis, and grain size determination in barley.
• HvABCD2 complemented all tested Arabidopsis cts-1 mutant phenotypes.
• HvABCD1 partially complemented seed size and IBA sensitivity but not germination/establishment in Arabidopsis, and complemented yeast beta-oxidation.
• Core biochemical functions of peroxisomal ABC transporters are conserved but physiological roles differ.

Conclusions:

• HvABCD1 and HvABCD2 play significant roles in barley metabolism and development.
• Functional conservation of peroxisomal ABC transporters exists between oilseed and cereal plants.
• Specific physiological roles and importance of these transporters can diverge between plant species.