title: Simultaneous knock-down of six β-galactosidase genes in petunia petals prevents loss of pectic galactan but decreases petal strength.
abstract: Galactose (Gal) is incorporated into cell wall polysaccharides as flowers open, but then is lost because of β-galactosidase activity as flowers mature and wilt. The significance of this for flower physiology resides in the role of galactan-containing polysaccharides in the cell wall, which is still largely unresolved. To investigate this, transcript accumulation of six cell wall-associated β-galactosidases was simultaneously knocked down in 'Mitchell' petunia (Petunia axillaris x (P. axillaris x P. hybrida)) flower petals. The multi-PhBGAL RNAi construct targeted three bud- and three senescence-associated β-galactosidase genes. The petals of the most down-regulated line (GA19) were significantly disrupted in galactose turnover during flower opening, and at the onset of senescence had retained 86% of their galactose compared with 20% in the controls. The Gal content of Na2CO3-soluble cell wall extracts and the highly insoluble polysaccharides associated with cellulose were particularly affected. Immunodetection with the antibody LM5 showed that much of the cell wall Gal in GA19 was retained as galactan, presumably the side-chains of rhamnogalacturonan-I. The flowers of GA19, despite having retained substantially more galactan, were no different from controls in their internal cell arrangement, dimensions, weight or timing of opening and senescence. However, the GA19 petals had less petal integrity (as judged by force required to cause petal fracture) after opening and showed a greater decline in this integrity with time than controls, raising the possibility that galactan loss is a mechanism for helping to maintain petal tissue cohesion after flower opening.
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Palmerston North, 4442, New Zealand. Electronic address: Erin.ODonoghue@plantandfood.co.nz.
authors.forename: Erin M
authors.initials: EM
authors.lastname: O'Donoghue
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Palmerston North, 4442, New Zealand.
authors.forename: Sheryl D
authors.initials: SD
authors.lastname: Somerfield
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Palmerston North, 4442, New Zealand.
authors.forename: Simon C
authors.initials: SC
authors.lastname: Deroles
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Mount Albert Research Centre, Auckland, 1142, New Zealand.
authors.forename: Paul W
authors.initials: PW
authors.lastname: Sutherland
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Mount Albert Research Centre, Auckland, 1142, New Zealand.
authors.forename: Ian C
authors.initials: IC
authors.lastname: Hallett
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Palmerston North, 4442, New Zealand.
authors.forename: Zoë A
authors.initials: ZA
authors.lastname: Erridge
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Palmerston North, 4442, New Zealand.
authors.forename: David A
authors.initials: DA
authors.lastname: Brummell
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Food Industry Science Centre, Palmerston North, 4442, New Zealand.
authors.forename: Donald A
authors.initials: DA
authors.lastname: Hunter
mesh_terms: D000375:Aging / Q000502:physiology; D001483:Base Sequence; D002254:Carbonates / Q000737:chemistry; D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism; D015536:Down-Regulation; D035264:Flowers / Q000737:chemistry / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D005685:Galactans / Q000378:metabolism*; D005690:Galactose / Q000378:metabolism; D055785:Gene Knockdown Techniques; D010368:Pectins / Q000378:metabolism*; D032306:Petunia / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D010936:Plant Extracts / Q000737:chemistry; D030821:Plants, Genetically Modified; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism
chemical_list: D002254:Carbonates; D005685:Galactans; D010936:Plant Extracts; D011134:Polysaccharides; C042491:rhamnogalacturonan I; C005686:sodium carbonate; D010368:Pectins; D001616:beta-Galactosidase; D005690:Galactose
keywords: Galactan; Galactosidase; Pectin; Petal; Petunia; Senescence