Control of germination and lipid mobilization by COMATOSE, the Arabidopsis homologue of human ALDP

Abstract

S.Footitt, S.P.Slocombe and V.Larner contributed equally to this workEmbryo dormancy in¯owering plants is an important dispersal mechanism that promotes survival of the seed through time. The subsequent transition to germination is a critical control point regulating initiation of vegetative growth. Here we show that the Arabidopsis COMATOSE (CTS) locus is required for this transition, and acts, at least in part, by profoundly affecting the metabolism of stored lipids. CTS encodes a peroxisomal protein of the ATP binding cassette (ABC) transporter class with signi®cant identity to the human X-linked adrenoleukodystrophy protein (ALDP). Like X-ALD patients, cts mutant embryos and seedlings exhibit pleiotropic phenotypes associated with perturbation in fatty acid metabolism. CTS expression transiently increases shortly after imbibition during germination, but not in imbibed dormant seeds, and genetic analyses show that CTS is negatively regulated by loci that promote embryo dormancy through multiple independent pathways. Our results demonstrate that CTS regulates transport of acyl CoAs into the peroxisome, and indicate that regulation of CTS function is a major control point for the switch between the opposing developmental programmes of dormancy and germination.

A key role for the peroxisomalABCD2transporter in fatty acid homeostasis

“…The same is true for worms and insectae; only one ABCD halfway between ABCD1 and ABCD2 can be found in their genomes. Plants, here represented by Oryza sativa and Arabidopsis thaliana, do not have any ABCD1-ABCD2 homologue; their closest ABCD, the comatose protein, is more similar to ABCD3 than to ABCD1 in contrast to previous reports (13). Fungi have two ABCD related proteins: Pxa2p and Pxa1p, which appear closer to ABCD1-2 than to ABCD3 or ABCD4, although they are more similar to one another than to any metazoan ABCD ( Fig.…”

On the role of a Lipid-Transfer Protein. Arabidopsis ltp3 mutant is compromised in germination and seedling growth.

“…35 In A. thaliana, 3 independent experimental approaches have identified the same peroxisomal transporter, named CTS /PXA1/PED3, as responsible for the translocation of at least part of the fatty acids for b-oxidation. 31,38,39 It has been suggested that CTS /PXA1/PED3 might not be the only transporter for b-oxidation substrates into the peroxisome 34 and a LTP may be reasonable implicated in this process. A mayor concern to consider this hypothesis is the subcellular location of LTP3.…”

The COMATOSE ATP-Binding Cassette Transporter Is Required for Full Fertility in Arabidopsis

“…Following mechanical rupture of the testa and seedling establishment in the presence of exogenous Suc, cts mutants can be transferred to soil and complete the life cycle (Russell et al, 2000;Footitt et al, 2002). However, mutation of CTS had subtle effects on vegetative growth: Rosette leaf number and area were reduced in cts-1 mutants compared to the wild type, Landsberg erecta (Ler), but these parameters were much less affected in cts-2 mutants, which more closely resembled the wild type, Wassilewskija2 (Ws2; Supplemental Fig.…”

“…Isolation of cts-1 and cts-2 has been described previously (Footitt et al, 2002). Seeds of kat2-1 and lacs6-1,lacs7-1 were the kind gifts of Professor Steve Smith (University of Western Australia) and Dr. Martin Fulda (University of Gö ttingen), respectively.…”

“…COMATOSE (CTS; also known as PEROXISOME DEFECTIVE3 [PED3] and A. thaliana PEROXISOMAL ABC TRANSPORTER1 [AtPXA1]) encodes a peroxisomal ATP-binding cassette transporter, which was identified in a genetic screen for positive regulators of germination (Russell et al, 2000). cts-1 mutant seeds cannot germinate in the absence of classical dormancybreaking treatments and do not establish in the absence of an exogenous energy source because of their inability to mobilize storage lipids by b-oxidation (Footitt et al, 2002(Footitt et al, , 2006. Mutant cts alleles have also been identified in screens for seedlings resistant to 2,4-dichlorophenoxybutyric acid and indole butyric acid (IBA; Zolman et al, 2001;Hayashi et al, 2002).…”