title: Tissue-specific transcriptome analysis reveals cell wall metabolism, flavonol biosynthesis and defense responses are activated in the endosperm of germinating Arabidopsis thaliana seeds.
abstract: Seed germination is a result of the competition of embryonic growth potential and mechanical constraint by surrounding tissues such as the endosperm. To understand the processes occurring in the endosperm during germination, we analyzed tiling array expression data on dissected endosperm and embryo from 6 and 24 h-imbibed Arabidopsis seeds. The genes preferentially expressed in the endosperm of both 6 and 24 h-imbibed seeds were enriched for those related to cell wall biosynthesis/modifications, flavonol biosynthesis, defense responses and cellular transport. Loss of function of AtXTH31/XTR8, an endosperm-specific gene for a putative xyloglucan endotransglycosylase/hydrolase, led to faster germination. This suggests that AtXTH31/XTR8 is involved in the reinforcement of the cell wall of the endosperm during germination. In vivo flavonol staining by diphenyl boric acid aminoethyl ester (DPBA) showed flavonols accumulated in the endosperm of both dormant and non-dormant seeds, suggesting that this event is independent of germination. Notably, DPBA fluorescence was also intense in the embryo, but the fluorescent region was diminished around the radicle and lower half of the hypocotyl during germination. DPBA fluorescence was localized in the vacuoles during germination. Vacuolation was not seen in imbibed dormant seeds, suggesting that vacuolation is associated with germination. A gene for δVPE (vacuolar processing enzyme), a caspase-1-like cysteine proteinase involved in cell death, is expressed specifically in endosperms of 24 h-imbibed seeds. The δvpe mutant showed retardation of vacuolation, but this mutation did not affect the kinetics of germination. This suggests that vacuolation is a consequence, and not a trigger, of germination.
authors.affiliation: Department of Cell & Systems Biology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Akira
authors.initials: A
authors.lastname: Endo
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Tatematsu
authors.forename: Kousuke
authors.initials: K
authors.lastname: Hanada
authors.forename: Lisza
authors.initials: L
authors.lastname: Duermeyer
authors.forename: Masanori
authors.initials: M
authors.lastname: Okamoto
authors.forename: Keiko
authors.initials: K
authors.lastname: Yonekura-Sakakibara
authors.forename: Kazuki
authors.initials: K
authors.lastname: Saito
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Toyoda
authors.forename: Naoto
authors.initials: N
authors.lastname: Kawakami
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamiya
authors.forename: Motoaki
authors.initials: M
authors.lastname: Seki
authors.forename: Eiji
authors.initials: E
authors.lastname: Nambara
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000196:embryology / Q000235:genetics* / Q000276:immunology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002473:Cell Wall / Q000235:genetics / Q000378:metabolism*; D056625:Endosperm / Q000166:cytology / Q000235:genetics*; D044948:Flavonols / Q000096:biosynthesis*; D005453:Fluorescence; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D018525:Germination / Q000235:genetics*; D058977:Molecular Sequence Annotation; D009928:Organ Specificity / Q000235:genetics; D013997:Time Factors; D014617:Vacuoles / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D044948:Flavonols