Ethylene

From Purdue Genomics Database Facility

Tomomichi Fujita (tfujita@sci.hokudai.ac.jp), Yuji Hiwatashi, Ryo Sotooka, Takeshi Maruyama, Tomoaki Nishiyama (tomakin@kenroku.kanazawa-u.ac.jp)

Contents 1 Biosynthesis 2 Signalling 3 References 4 Table of gene numbers

Biosynthesis

Ethylene is produced in all land plants previously examined, which includes lycopods and mosses (Davies, 2004). In seed plants, ethylene is synthesized from methionine through the intermediated S-adenosyl methionine and 1-aminocyclopropane-1-carboxylic acid (ACC), commonly called the ACC pathway. ACC synthase and ACC oxidase are key enzymes responsible for the ACC pathway. Biochemical studies have suggested the lack of ACC pathway in a fern and a liverwort, because of a lack of the ability to convert ACC into ethylene (Osborne et al. 1996).

The key ethylene biosynthetic enzymes ACC synthase and ACC oxidase genes, ACSs and ACOs, were not found in S. moellendorffii and P. patens, which is consistent with the biochemical data (Osborne et al. 1996), This implies that S. moellendorffii and P. patens produce ethylene with a distinct pathway from that of angiosperms.

RCN1 is proposed to act in hypocotyl elongation through the regulation of ethylene biosynthesis and auxin transport (Muday et al. 2006). Putative orthologues of RCN1 are found in all of the four lineages.

Signalling

We found potential orthologs for signaling factors of ethylene in all the vascular plants; receptors (ETR1 and ERS1), its signaling regulators (CTR1, EIN2, EBF1/2), and the downstream transcription factors (EIN3 and their paralogs, EIL1-EIL5). P. patens, however, lacks a potential ortholog of CTR1 though it has all the other orthologs for the ethylene signaling. This may explain the facts that bryophytes seem to have no unambiguous ethylene response while ferns show ethylene response (Raghavan, 1989).

References

Davies, P.J. (2004). Plant hormones. (Dordrecht, Netherland: Kluwer Academic Publishers).

Muday, G.K., Brady, S.R., Argueso, C., Deruere, J., Kieber, J.J., and DeLong, A. (2006). RCN1-regulated phosphatase activity and EIN2 modulate hypocotyl gravitropism by a mechanism that does not require ethylene signaling. Plant Physiol 141, 1617-1629.

Osborne, D.J., Walters, J., Milborrow, B.V., Norville, A., and Stange, L.M.C. (1996). Evidence for a non-ACC ethylene biosynthesis pathway in lower plants. Phytochemistry 42, 51-60.

Raghavan, V. (1989). Developmental Biology of Fern Gametophytes. (Cambridge: Cambridge Univ. Press).

Table of gene numbers

Gene functions	Gene	Gene used as a query	The number of putative orthologs
			Arabidopsis thaliana	Oryza sativa	Selaginalla moellendorffii	Physcomitrella patens
Ethylene biosynthesis	ACS1 to 9, and 11	ACS2	10	5	0	0
Ethylene biosynthesis	ACO1 and 2	ACO2	5	7	0	0
Regulation of ethylene biosynthesis	RCN1	RCN1	3	1	2 (4)	4
Ethylen signalling	ETR1 and ERS1	ETR1	2	2	3 (6)	4
Ethylen signalling	ETR2, ERS2, and EIN4	ETR1	3	3	0	1
Ethylen signalling	CTR1	CTR1	6	8	4 (6)	0
Ethylen signalling	EIN2	EIN2	1	3	1	1
Ethylen signalling	EBF1 and 2	EBF1	2	2	2 (2)	2