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One week after partial incision of Arabidopsis inflorescence stems, the repair process in damaged tissue includes pith cell proliferation. Auxin is a key factor driving this process, and ANAC071, a transcription factor gene, is upregulated in the distal region of the incised stem. Here we show that XTH20 and the closely related XTH19, members of xyloglucan endotransglucosylase/hydrolases family catalyzing molecular grafting and/or hydrolysis of cell wall xyloglucans, were also upregulated in the distal part of the incised stem, similar to ANAC071. XTH19 was expressed in the proximal incision region after 3 days or after auxin application to the decapitated stem. Horizontal positioning of the plant with the incised side up resulted in decreased Pro DR 5 : GUS, ANAC071, XTH20, and XTH19 expression and reduced pith cell proliferation. In incised stems of Pro 35S : ANAC071- SRDX plants, expression of XTH20 and XTH19 was substantially and moderately decreased, respectively. XTH20 and XTH19 expression and pith cell proliferation were suppressed in anac071 plants and were increased in Pro 35S : ANAC071 plants. Pith cell proliferation was also inhibited in the xth20xth19 double mutant. Furthermore, ANAC071 bound to the XTH20 and XTH19 promoters to induce their expression. This study revealed XTH20 and XTH19 induction by auxin via ANAC071 in the distal part of an incised stem and their involvement in cell proliferation in the tissue reunion process. [ABSTRACT FROM AUTHOR]

This comprehensive overview of the xyloglucan endotransglucosylase/hydrolase (XTH) family of genes and proteins in bryophytes, based on research using genomic resources that are newly available for the moss Physcomitrella patens, provides new insights into plant evolution. In angiosperms, the XTH genes are found in large multi-gene families, probably reflecting the diverse roles of individual XTHs in various cell types. As there are fewer cell types in P. patens than in angiosperms such as Arabidopsis and rice, it is tempting to deduce that there are fewer XTH family genes in bryophytes. However, the present study unexpectedly identified as many as 32 genes that potentially encode XTH family proteins in the genome of P. patens, constituting a fairly large multi-gene family that is comparable in size with those of Arabidopsis and rice. In situ localization of xyloglucan endotransglucosylase activity in this moss indicates that some P. patens XTH proteins exhibit biochemical functions similar to those found in angiosperms, and that their expression profiles are tissue-dependent. However, comparison of structural features of families of XTH genes between P. patens and angiosperms demonstrated the existence of several bryophyte-specific XTH genes with distinct structural and functional features that are not found in angiosperms. These bryophyte-specific XTH genes might have evolved to meet morphological and functional needs specific to the bryophyte. These findings raise interesting questions about the biological implications of the XTH family of proteins in non-seed plants. [ABSTRACT FROM AUTHOR]

Arabidopsis root hair formation is determined by the patterning genes CAPRICE ( CPC), GLABRA3 ( GL3), WEREWOLF ( WER) and GLABRA2 ( GL2), but little is known about the later changes in cell wall material during root hair formation. A combined Fourier-transform infrared microspectroscopy–principal components analysis (FTIR-PCA) method was used to detect subtle differences in the cell wall material between wild-type and root hair mutants in Arabidopsis. Among several root hair mutants, only the gl2 mutation affected root cell wall polysaccharides. Five of the 10 genes encoding cellulose synthase ( CESA1– 10) and 4 of 33 xyloglucan endotransglucosylase ( XTH1– 33) genes in Arabidopsis are expressed in the root, but only CESA5 and XTH17 were affected by the gl2 mutation. The L1-box sequence located in the promoter region of these genes was recognized by the GL2 protein. These results indicate that GL2 directly regulates cell wall-related gene expression during root development. [ABSTRACT FROM AUTHOR]

Xyloglucan endotransglucosylases/hydrolases (XTHs) are a class of enzymes capable of catalyzing the molecular grafting between xyloglucans and/or the endotype hydrolysis of a xyloglucan molecule. They are encoded by 33 genes in Arabidopsis. Whereas recent studies have revealed temporally and spatially specific expression profiles for individual members of this family in plants, their biological roles are still to be clarified. To identify the role of each member of this gene family, we examined phenotypes of mutants in which each of the ArabidopsisXTHgenes was disrupted. This was undertaken using a reverse genetic approach, and disclosed two loss-of-function mutants for theAtXTH27gene,xth27-1andxth27-2. These exhibited short-shaped tracheary elements in tertiary veins, and reduced the number of tertiary veins in the first leaf. In mature rosette leaves of the mutant, yellow lesion-mimic spots were also observed. Upon genetic complementation by introducing the wild-typeXTH27gene intoxth27-1mutant plants, the number of tertiary veins was restored, and the lesions disappeared completely. Extensive expression of the pXTH27::GUSfusion gene was observed in immature tracheary elements in the rosette leaves. The highest level ofAtXTH27mRNA expression in the rosette leaves was observed during leaf expansion, when the tracheary elements were elongating. These findings indicate thatAtXTH27plays an essential role during the generation of tracheary elements in the rosette leaves of Arabidopsis. [ABSTRACT FROM AUTHOR]

Summary:InArabidopsis thaliana(L.) Heynh, the mutation inERECTAis known to confer a compact inflorescence by a reduction in the lengths of internodes and pedicels. We analyzed the expression pattern of this gene during plant development.In situhybridization and histochemical analysis using transgenic plants carrying chimeric gene fusions, with theERECTApromoter fused to the β-glucuronidase (GUS) gene, showed thatERECTAwas predominantly expressed in the shoot apical meristems and organ primordia.ERECTAexpression in the shoot apical meristem was weak early in plant development but increased with the transition from the vegetative to the reproductive growth phase.ERECTAwas also strongly expressed in organ primordia and immature organs but weakly in mature organs. Thus,ERECTAwas expressed in a cell-specific and developmentally regulated manner. In order to identify the regulatory mechanism responsible for the expression pattern ofERECTA, thecis-acting regions in theERECTApromoter were defined by study of the expression of the chimeric genes that consist of the 5′- or internal deleted promoter and a GUS reporter gene in transgenic plants. The results showed that the essentialcis-regulatory elements governing the spatially and temporally specific expression ofERECTAare located between positions –462 and – 228 bp and between positions –228 and –153 bp with respect to the transcriptional initiation site.. [ABSTRACT FROM AUTHOR]