Gene Expression Profiling Reveals Defined Functions of the ATP-Binding Cassette Transporter COMATOSE Late in Phase II of Germination

Esther Carrera,Wendy Peer,Heike Schmuths,Tara Holman,Frederica L. Theodoulou,Michael J. Holdsworth,Steven Footitt,Anne Medhurst

doi:10.1104/pp.107.096057

Esther Carrera, Wendy Peer + Show 6 more

Open Access

https://doi.org/10.1104/pp.107.096057

Copy DOI

Abstract

Phase II of germination represents a key developmental stage of plant growth during which imbibed seeds either enter stage III of germination, completing the germination process via radicle protrusion, or remain dormant. In this study, we analyzed the influence of the peroxisomal ATP-binding cassette transporter COMATOSE (CTS) on the postimbibition seed transcriptome of Arabidopsis (Arabidopsis thaliana) and also investigated interactions between gibberellin (GA) and CTS function. A novel method for analysis of transcriptome datasets allowed visualization of developmental signatures of seeds, showing that cts-1 retains the capacity to after ripen, indicating a germination block late in phase II. Expression of the key GA biosynthetic genes GA3ox1 and 2 was greatly reduced in cts seeds and genetic analysis suggested that CTS was epistatic to RGL2, a germination-repressing DELLA protein that is degraded by GA. Comparative analysis of seed transcriptome datasets indicated that specific cohorts of genes were influenced by GA and CTS. CTS function was required for expression of the flavonoid biosynthetic pathway. Confocal imaging demonstrated the exclusive accumulation of flavonoids in the epidermis of wild-type seeds. In contrast, flavonoids were absent from cts and kat2-1 mutant seeds, but accumulated following the application of sucrose, indicating an essential role for beta-oxidation in inducing flavonoid biosynthetic genes. These results demonstrate that CTS functions very late in phase II of germination and that its function is required for the expression of specific gene sets related to an important biochemical pathway associated with seedling establishment and survival.

Highlights

Phase II of germination represents a key developmental stage of plant growth during which imbibed seeds either enter stage III of germination, completing the germination process via radicle protrusion, or remain dormant
CTS is a single-copy gene encoding a full-length ATP-binding cassette transporter that is required for the import of several biologically important molecules into the peroxisome, including very-long-chain fatty acids associated with breakdown of seed-storage lipids, and precursors of auxin and jasmonic acid biosynthesis (Zolman et al, 2001; Footitt et al, 2002; Hayashi et al, 2002; Theodoulou et al, 2005)
We followed the frequency of testa and endosperm rupture in fully AR Landsberg erecta (Ler) wild-type seeds and showed that testa rupture occurs between 40 to 45 h and subsequent endosperm rupture occurs between 45 to 50 h (Fig. 1B)

Summary

Introduction

Phase II of germination represents a key developmental stage of plant growth during which imbibed seeds either enter stage III of germination, completing the germination process via radicle protrusion, or remain dormant. Comparison of signatures obtained from transcripts differentially regulated in imbibed cts-1 S seeds compared with cts-1 F seeds showed that these gene sets contained transcripts encoding genes of very different functions (Fig. 4D; Supplemental Table S1).

Results

Conclusion