title: Phosphate availability regulates ethylene biosynthesis gene expression and protein accumulation in white clover (Trifolium repens L.) roots.
abstract: The expression and accumulation of members of the 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase (ACO) gene families was examined in white clover roots grown in either Pi(phosphate) sufficient or Pi-deprived defined media. The accumulation of one ACO isoform, TR-ACO1, was positively influenced after only 1 h of exposure to low Pi, and this was maintained over a 7-day time-course. Up-regulation of TR-ACS1, TR-ACS2 and TR-ACS3 transcript abundance was also observed within 1 h of exposure to low Piin different tissue regions of the roots, followed by a second increase in abundance of TR-ACS2 after 5-7 days of exposure. An increase in transcript abundance of TR-ACO1 and TR-ACO3, but not TR-ACO2, was observed after 1 h of exposure to low Pi, with a second increase in TR-ACO1 transcripts occurring after 2-5 days. These initial increases of the TR-ACS and TR-ACO transcript abundance occurred before the induction of Trifolium repens PHOSPHATE TRANSPORTER 1 (TR-PT1), and the addition of sodium phosphite did not up-regulate TR-ACS1 expression over 24 h. In situ hybridization revealed some overlap of TR-ACO mRNA accumulation, with TR-ACO1 and TR-ACO2 in the root tip regions, and TR-ACO1 and TR-ACO3 mRNA predominantly in the lateral root primordia. TR-ACO1p-driven GFP expression showed that activation of the TR-ACO1 promoter was initiated within 24 h of exposure to low Pi(as determined by GFP protein accumulation). These results suggest that the regulation of ethylene biosynthesis in white clover roots is biphasic in response to low Pisupply.
authors.affiliation: Institute of Fundamental Sciences, Massey University, Private Bag 11222, Palmerston North 4474, New Zealand marissa.roldan@agresearch.co.nz.
authors.forename: Marissa
authors.initials: M
authors.lastname: Roldan
authors.affiliation: Institute of Fundamental Sciences, Massey University, Private Bag 11222, Palmerston North 4474, New Zealand.
authors.forename: Afsana
authors.initials: A
authors.lastname: Islam
authors.affiliation: Institute of Fundamental Sciences, Massey University, Private Bag 11222, Palmerston North 4474, New Zealand.
authors.forename: Phuong T Y
authors.initials: PTY
authors.lastname: Dinh
authors.affiliation: Institute of Fundamental Sciences, Massey University, Private Bag 11222, Palmerston North 4474, New Zealand.
authors.forename: Susanna
authors.initials: S
authors.lastname: Leung
authors.affiliation: Institute of Fundamental Sciences, Massey University, Private Bag 11222, Palmerston North 4474, New Zealand.
authors.forename: Michael T
authors.initials: MT
authors.lastname: McManus
mesh_terms: D005030:Ethylenes / Q000096:biosynthesis*; D015870:Gene Expression / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D017343:Genes, Plant / Q000235:genetics; D008190:Lyases / Q000235:genetics; D010088:Oxidoreductases / Q000235:genetics; D010710:Phosphates / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D029921:Trifolium / Q000235:genetics*; D015854:Up-Regulation / Q000235:genetics
chemical_list: D005030:Ethylenes; D010710:Phosphates; D012333:RNA, Messenger; D010088:Oxidoreductases; D008190:Lyases; C021773:1-aminocyclopropanecarboxylate synthase
keywords: ACC oxidase; ACC synthase; ethylene biosynthesis; phosphate supply; plant roots; transcriptional regulation