ABSTRACT
Maturation-related changes in cell wall composition and the molecular mechanisms underlying cell wall changes were investigated from the apical, middle and basal segments in moso bamboo shoot (MBS). With maturation extent from apical to basal regions in MBS, lignin and cellulose content increased, whereas heteroxylan exhibited a decreasing trend. Activities of phenylalanine amonnialyase (PAL), cinnamyl alcohol dehydrogenase (CAD) and cinnamate-4-hydroxylase (C4H), which are involved in lignin biosynthesis, increased rapidly from the apex to the base sections. The comparative transcriptomic analysis was carried out to identify some key genes involved in secondary cell walls (SCW) formation underlying the cell wall compositions changes including 63, 8, 18, and 31 functional unigenes encoding biosynthesis of lignin, cellulose, xylan and NAC-MYB-based transcription factors, respectively. Genes related to secondary cell wall formation and lignin biosynthesis had higher expression levels in the middle and basal segments compared to those in the apical segments. Furthermore, the expression profile of PePAL gene showed positive relationships with cellulose-related gene PeCESA4, xylan-related genes PeIRX9 and PeIRX10. Our results indicated that lignification occurred in the more mature middle and basal segments in MBS at harvest while lignification of MBS were correlated with higher expression levels of PeCESA4, PeIRX9 and PeIRX10 genes.
Subject(s)
Bambusa/growth & development , Plant Proteins/genetics , Plant Shoots/metabolism , RNA, Plant/genetics , Transcriptome , Bambusa/geneticsABSTRACT
Xylan is the major plant hemicellulosic polysaccharide in the secondary cell wall. The transcription factor KNOTTED-LIKE HOMEOBOX OF ARABIDOPSIS THALIANA 7 (KNAT7) regulates secondary cell wall biosynthesis, but its exact role in regulating xylan biosynthesis remains unclear. Using transactivation analyses, we demonstrate that KNAT7 activates the promoters of the xylan biosynthetic genes, IRREGULAR XYLEM 9 (IRX9), IRX10, IRREGULAR XYLEM 14-LIKE (IRX14L), and FRAGILE FIBER 8 (FRA8). The knat7 T-DNA insertion mutants have thinner vessel element walls and xylary fibers, and thicker interfascicular fiber walls in inflorescence stems, relative to wild-type (WT). KNAT7 overexpression plants exhibited opposite effects. Glycosyl linkage and sugar composition analyses revealed lower xylan levels in knat7 inflorescence stems, relative to WT; a finding supported by labeling of inflorescence walls with xylan-specific antibodies. The knat7 loss-of-function mutants had lower transcript levels of the xylan biosynthetic genes IRX9, IRX10, and FRA8, whereas KNAT7 overexpression plants had higher mRNA levels for IRX9, IRX10, IRX14L, and FRA8. Electrophoretic mobility shift assays indicated that KNAT7 binds to the IRX9 promoter. These results support the hypothesis that KNAT7 positively regulates xylan biosynthesis.
Subject(s)
Arabidopsis Proteins/genetics , Arabidopsis Proteins/metabolism , Arabidopsis/genetics , Arabidopsis/metabolism , Gene Expression Regulation, Plant , Pentosyltransferases/genetics , Repressor Proteins/metabolism , Xylans/biosynthesis , Biosynthetic Pathways/genetics , Cell Wall/metabolism , Gene Expression Profiling , Inflorescence/genetics , Models, Biological , Mutation/genetics , Plants, Genetically Modified , Promoter Regions, Genetic , Protein Binding/genetics , Sugars/metabolismABSTRACT
Recent studies indicate that the ETHYLENE RESPONSE FACTOR VII (ERF-VII) transcription factor is an important regulator of osmotic and hypoxic stress responses in plants. However, the molecular mechanism of ERF-VII-mediated transcriptional regulation remains unclear. Here, we investigated the role of ERF74 (a member of the ERF-VII protein family) by examining the abiotic stress tolerance of an ERF74 overexpression line and a T-DNA insertion mutant using flow cytometry, transactivation and electrophoretic mobility shift assays. 35S::ERF74 showed enhanced tolerance to drought, high light, heat and aluminum stresses, whereas the T-DNA insertion mutant erf74 and the erf74;erf75 double mutant displayed higher sensitivity. Using flow cytometry analysis, we found that erf74 and erf74;erf75 lines lack the reactive oxygen species (ROS) burst in the early stages of various stresses, as a result of the lower expression level of RESPIRATORY BURST OXIDASE HOMOLOG D (RbohD). Furthermore, ERF74 directly binds to the promoter of RbohD and activates its expression under different abiotic stresses. Moreover, induction of stress marker genes and ROS-scavenging enzyme genes under various stress conditions is dependent on the ERF74-RbohD-ROS signal pathway. We propose a pathway that involves ERF74 acting as an on-off switch controlling an RbohD-dependent mechanism in response to different stresses, subsequently maintaining hydrogen peroxide (H2 O2 ) homeostasis in Arabidopsis.
