α-Xylosidase plays essential roles in xyloglucan remodelling, maintenance of cell wall integrity, and seed germination in Arabidopsis thaliana.
Regulation and maintenance of cell wall physical properties are crucial for plant growth and environmental response. In the germination process, hypocotyl cell expansion and endosperm weakening are prerequisites for dicot seeds to complete germination. We have identified the Arabidopsis mutant thermoinhibition-resistant germination 1 (trg1), which has reduced seed dormancy and insensitivity to unfavourable conditions for germination owing to a loss-of-function mutation of TRG1/XYL1, which encodes an α-xylosidase. Compared to those of wild type, the elongating stem of trg1 showed significantly lower viscoelasticity, and the fruit epidermal cells were longitudinally shorter and horizontally enlarged. Actively growing tissues of trg1 over-accumulated free xyloglucan oligosaccharides (XGOs), and the seed cell wall had xyloglucan with a greatly reduced molecular weight. These observations suggest that XGOs reduce xyloglucan size by serving as an acceptor in transglycosylation and eventually enhancing cell wall loosening. TRG1/XYL1 gene expression was abundant in growing wild-type organs and tissues but relatively low in cells at most actively elongating part of the tissues, suggesting that α-xylosidase contributes to maintaining the mechanical integrity of the primary cell wall in the growing and pre-growing tissues. In germinating seeds of trg1, expression of genes encoding specific abscisic acid and gibberellin metabolism enzymes was altered in accordance with the aberrant germination phenotype. Thus, cell wall integrity could affect seed germination not only directly through the physical properties of the cell wall but also indirectly through the regulation of hormone gene expression.
Department of Life Sciences, School of Agriculture, Meiji University, Higashimita 1-1-1, Tama-ku, Kawasaki 214-8571, Japan.
Takuma
T
Shigeyama
Department of Life Sciences, School of Agriculture, Meiji University, Higashimita 1-1-1, Tama-ku, Kawasaki 214-8571, Japan.
Asuka
A
Watanabe
Department of Life Sciences, School of Agriculture, Meiji University, Higashimita 1-1-1, Tama-ku, Kawasaki 214-8571, Japan.
Konatsu
K
Tokuchi
Department of Life Sciences, School of Agriculture, Meiji University, Higashimita 1-1-1, Tama-ku, Kawasaki 214-8571, Japan.
Shigeo
S
Toh
Graduate School of Biosphere Science, Hiroshima University, Kagamiyama 1-3-2, Higashihiroshima 739-8528, Japan.
Naoki
N
Sakurai
Department of Life Sciences, School of Agriculture, Meiji University, Higashimita 1-1-1, Tama-ku, Kawasaki 214-8571, Japan.
Naoto
N
Shibuya
Department of Life Sciences, School of Agriculture, Meiji University, Higashimita 1-1-1, Tama-ku, Kawasaki 214-8571, Japan kawakami@meiji.ac.jp.
Naoto
N
Kawakami
D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism* / Q000502:physiology; D002473:Cell Wall / Q000378:metabolism* / Q000502:physiology; D020869:Gene Expression Profiling; D018525:Germination / Q000502:physiology*; D005936:Glucans / Q000378:metabolism*; D057445:Plant Dormancy / Q000502:physiology; D030821:Plants, Genetically Modified; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012639:Seeds / Q000254:growth & development* / Q000378:metabolism; D014990:Xylans / Q000378:metabolism*; D014995:Xylosidases / Q000378:metabolism / Q000502:physiology*
D005936:Glucans; D014990:Xylans; C029353:xyloglucan; D014995:Xylosidases; C047831:alpha-D-xylosidase
Abscisic acid; cell wall; gibberellin; seed dormancy; thermoinhibition; xyloglucan oligosaccharide.