title: Temporal and spatial expression of polygalacturonase gene family members reveals divergent regulation during fleshy fruit ripening and abscission in the monocot species oil palm.
abstract: BACKGROUND
  Cell separation that occurs during fleshy fruit abscission and dry fruit dehiscence facilitates seed dispersal, the final stage of plant reproductive development. While our understanding of the evolutionary context of cell separation is limited mainly to the eudicot model systems tomato and Arabidopsis, less is known about the mechanisms underlying fruit abscission in crop species, monocots in particular. The polygalacturonase (PG) multigene family encodes enzymes involved in the depolymerisation of pectin homogalacturonan within the primary cell wall and middle lamella. PG activity is commonly found in the separation layers during organ abscission and dehiscence, however, little is known about how this gene family has diverged since the separation of monocot and eudicots and the consequence of this divergence on the abscission process.
  
  
  RESULTS
  The objective of the current study was to identify PGs responsible for the high activity previously observed in the abscission zone (AZ) during fruit shedding of the tropical monocot oil palm, and to analyze PG gene expression during oil palm fruit ripening and abscission. We identified 14 transcripts that encode PGs, all of which are expressed in the base of the oil palm fruit. The accumulation of five PG transcripts increase, four decrease and five do not change during ethylene treatments that induce cell separation. One PG transcript (EgPG4) is the most highly induced in the fruit base, with a 700-5000 fold increase during the ethylene treatment. In situ hybridization experiments indicate that the EgPG4 transcript increases preferentially in the AZ cell layers in the base of the fruit in response to ethylene prior to cell separation.
  
  
  CONCLUSIONS
  The expression pattern of EgPG4 is consistent with the temporal and spatial requirements for cell separation to occur during oil palm fruit shedding. The sequence diversity of PGs and the complexity of their expression in the oil palm fruit tissues contrast with data from tomato, suggesting functional divergence underlying the ripening and abscission processes has occurred between these two fruit species. Furthermore, phylogenetic analysis of EgPG4 with PGs from other species suggests some conservation, but also diversification has occurred between monocots and eudicots, in particular between dry and fleshy fruit species.
authors.affiliation: Institut de Recherche pour le Développement, IRD Centre de Montpellier, IRD/CIRAD Palm Development Group, DIADE 911 avenue agropolis BP 64501, 34394 Montpellier cedex 5, France.
authors.forename: Peerapat
authors.initials: P
authors.lastname: Roongsattham
authors.forename: Fabienne
authors.initials: F
authors.lastname: Morcillo
authors.forename: Chatchawan
authors.initials: C
authors.lastname: Jantasuriyarat
authors.forename: Maxime
authors.initials: M
authors.lastname: Pizot
authors.forename: Steven
authors.initials: S
authors.lastname: Moussu
authors.forename: Dasuni
authors.initials: D
authors.lastname: Jayaweera
authors.forename: Myriam
authors.initials: M
authors.lastname: Collin
authors.forename: Zinnia H
authors.initials: ZH
authors.lastname: Gonzalez-Carranza
authors.forename: Philippe
authors.initials: P
authors.lastname: Amblard
authors.forename: James W
authors.initials: JW
authors.lastname: Tregear
authors.forename: Somvong
authors.initials: S
authors.lastname: Tragoonrung
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Verdeil
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Tranbarger
mesh_terms: D028023:Arecaceae / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D005030:Ethylenes / Q000494:pharmacology; D005638:Fruit / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development*; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D017403:In Situ Hybridization; D008969:Molecular Sequence Data; D005810:Multigene Family; D000073878:Palm Oil; D010802:Phylogeny; D010938:Plant Oils / Q000378:metabolism; D011096:Polygalacturonase / Q000737:chemistry / Q000235:genetics*; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013997:Time Factors
chemical_list: D005030:Ethylenes; D010938:Plant Oils; D012333:RNA, Messenger; D000073878:Palm Oil; C036216:ethylene; D011096:Polygalacturonase