Disease relevance of TCH4

• We have produced four Arabidopsis XETs (TCH4, Meri-5, EXGT and XTR9) using the baculovirus/insect cell system and compared their biochemical activities [1].

High impact information on TCH4

• Proposed roles of XET that include cell wall loosening and integration of newly synthesized xyloglucans could thus be supported [2].
• We determined that TCH4 expression is regulated by auxin and brassinosteroids, by environmental stimuli, and during development, by a 1-kb region [3].
• Here, we show that induction of expression by the diverse stimuli of touch, darkness, cold, heat, and brassinosteroids (BRs) is conferred to reporter genes by the same 102-bp 5'-untranscribed TCH4 region; this result is consistent with the idea that shared regulatory elements are employed by diverse stimuli [4].
• However, 5'-untranslated sequences are necessary and sufficient to confer the marked transience of TCH4 expression, most likely through an effect on mRNA stability [4].
• The ethylene precursor 1-aminocyclopropane-1-carboxylic acid shifts both root hair initiation and the local increase in XET action toward the root tip [5].

Biological context of TCH4

• Co- and/or post-translational modifications are critical for TCH4 XET activity [6].
• These results indicate that TCH4 may contribute to the adaptive changes in morphogenesis that occur in Arabidopsis following exposure to mechanical stimuli [7].
• TCH4 is unlikely to play a role in acid-induced wall loosening but may function in cold acclimation or cold-tolerant growth [8].
• These data support the hypothesis that, in analogy to Bacillus beta-glucanases, this region may be the active site of XET enzymes [6].
• Therefore, XET function may affect cell shape and plant morphogenesis [6].

Anatomical context of TCH4

• Previous work has shown that the Arabidopsis TCH4 gene encodes a xyloglucan endotransglycosylase (XET) which acts on the major hemicellulose of the plant cell wall [9].
• TCH4 protein engineered to be synthesized in the cytosol and thus lack normal co- and post-translational modifications is virtually inactive [6].
• Disruption of actin and microtubules did not prevent the localized increase in XET action [5].

Associations of TCH4 with chemical compounds

• The expression of TCH4 is dramatically upregulated in response to several environmental stimuli (including touch, wind, darkness, heat shock, and cold shock) as well as the growth-enhancing hormones, auxin and brassinosteroids [9].
• TCH4 proteins, with and without a polyhistidine tag, that harbor an intact N-terminus are directed to the secretory pathway [6].
• The Arabidopsis TCH4 xyloglucan endotransglycosylase. Substrate specificity, pH optimum, and cold tolerance [8].
• TCH4 is shown to have at least one disulfide bond as monitored by a mobility shift in SDS-PAGE in the presence of dithiothreitol (DTT) [6].
• TCH4 is most active at pH 6.0 to 6.5 and is surprisingly cold-tolerant with an optimum of 12 to 18 degrees C. TCH4 activity is enhanced by urea and bovine serum albumin, but nor cations, reducing agents, or carboxymethylcellulose [8].

Other interactions of TCH4

• In addition to TCH4, this family includes two previously identified genes, EXT and Meri-5, and at least five additional genes [9].
• Involvement of the xyloglucan endotransglycosylase/hydrolases encoded by celery XTH1 and Arabidopsis XTH33 in the phloem response to aphids [10].
• The Arabidopsis TCH genes, which encode calmodulin-related proteins and a xyloglucan endotransglycosylase, are shown to be up-regulated in expression following cold shock [11].
• We demonstrated that hypergravity influenced the expression of some XTH genes in shoots of Arabidopsis thaliana L.; in response to hypergravity stimulus of 300 g, the expression of AtXTH22 was up-regulated, while that of AtXTH15 was down-regulated [12].
• Some of the selected genes on this microarray (e.g. Xyloglucan endotransglycosylase, At2g18800) showed differential expression both in Arabidopsis exposed to hypergravity and simulated hypogravity by use of a centrifuge and a Random Positioning Machine [13].

References