Xyloglucan endotransglycosylase (XET) is thought to be involved in fruit softening throughdisassembly of xyloglucan, which is the predominant hemicellulose of cell wall. To study the relationshipbetween fruit softenin...Xyloglucan endotransglycosylase (XET) is thought to be involved in fruit softening throughdisassembly of xyloglucan, which is the predominant hemicellulose of cell wall. To study the relationshipbetween fruit softening and XET during banana (Musa acuminata Colla cv. Grand Nain) fruit ripening, a fulllength cDNA (1 095 bp) encoding an XET, MA-XET1, was isolated from ripening banana fruit using RT-PCRand RACE-PCR (rapid amplification of cDNA ends) methods. Sequence analysis showed that the cDNAcontains 5' untranslated region of 66 bp, 3' untranslated region of 189 bp and ORF of 840 bp, encoding apredicted polypeptide of 280 amino acids, including DE|DFEFL motif, which is a presumptive catalyticdomain conserved in XETs. DNA gel blot analysis demonstrated that MA-XET1 is encoded by a multi-copyfamily in the banana genome. RNA gel blot analysis revealed that the level of MA-XET1 transcript in thepulp was undetectable, increased and decreased slightly at the preclimacteric, climacteric and postclimactericstages, respectively. In the peel, accumulation of MA-XET1 transcript was low, increased dramatically andthen decreased rapidly, at preclimacteric, climacteric and postclimacteric stages, respectively. Treatmentof fruit with propylene, an analog of ethylene, decreased the firmness and enhanced the accumulation ofMA-XET1 transcript in the peel and pulp. These results suggest that MA-XET1 is involved in softening ofthe peel and pulp during banana fruit ripening and its expression is regulated by ethylene at transcriptionallevel.展开更多
Radicle emergence and reserves mobilization are two distinct programmes that are thought to control germination. Both programs are influenced by abscissic acid （ABA） but how this hormone controls seed germination is...Radicle emergence and reserves mobilization are two distinct programmes that are thought to control germination. Both programs are influenced by abscissic acid （ABA） but how this hormone controls seed germination is still poorly known. Phenotypic and microscopic observations of the embryo axis of Medicago truncatula during germination in mitotic inhibition condition triggered by 10 μM oryzalin showed that cell division was not required to allow radicle emergence. A suppressive subtractive hybridization showed that more than 10% of up-regulated genes in the embryo axis encoded proteins related to cell-wall biosynthesis. The expression of α-expansins, pectin-esterase, xylogucan-endotransglycosidase, cellulose synthase, and extensins was monitored in the embryo axis of seeds germinated on water, constant and transitory ABA. These genes were overexpressed before completion of germination in the control and strongly inhibited by ABA. The expression was re-established in the ABA transitory-treatment after the seeds were transferred back on water and proceeded to germination. This proves these genes as contributors to the completion of germination and strengthen the idea that cell-wall loosening and remodeling in relation to cell expansion in the embryo axis is a determinant feature in germination. Our results also showed that ABA controls germination through the control of radicle emergence, namely by inhibiting cell-wall loosening and expansion.展开更多
Xyloglucan endotransglycosylase is an identified relaxation factor with functions of easing and extending of plant cell walls.Its activities are directly related to plant growth and elongation of organisms.Anthocephal...Xyloglucan endotransglycosylase is an identified relaxation factor with functions of easing and extending of plant cell walls.Its activities are directly related to plant growth and elongation of organisms.Anthocephalus chinensis is a tall and fast growing evergreen tree species.We cloned the full cDNA sequence of AcEXT genes which is abundantly expressed in the cambium of A.chinensis.The sequence analysis of nucleotides and amino acids revealed the presence of a 1396 bp full cDNA sequence,including a 960 bp complete open reading frame（ORF） encoding a 320 amino acid protein.The deduced amino acid sequence of AcXET was homologous to the other known XET proteins and contained the conserved EIDFE catalytic site which was specific to all the XETs.Our data should serve as a foundation for further insight into AcXET gene molecular mechanisms during wood formation and cell wall engineering of woody plants.展开更多
文摘Xyloglucan endotransglycosylase (XET) is thought to be involved in fruit softening throughdisassembly of xyloglucan, which is the predominant hemicellulose of cell wall. To study the relationshipbetween fruit softening and XET during banana (Musa acuminata Colla cv. Grand Nain) fruit ripening, a fulllength cDNA (1 095 bp) encoding an XET, MA-XET1, was isolated from ripening banana fruit using RT-PCRand RACE-PCR (rapid amplification of cDNA ends) methods. Sequence analysis showed that the cDNAcontains 5' untranslated region of 66 bp, 3' untranslated region of 189 bp and ORF of 840 bp, encoding apredicted polypeptide of 280 amino acids, including DE|DFEFL motif, which is a presumptive catalyticdomain conserved in XETs. DNA gel blot analysis demonstrated that MA-XET1 is encoded by a multi-copyfamily in the banana genome. RNA gel blot analysis revealed that the level of MA-XET1 transcript in thepulp was undetectable, increased and decreased slightly at the preclimacteric, climacteric and postclimactericstages, respectively. In the peel, accumulation of MA-XET1 transcript was low, increased dramatically andthen decreased rapidly, at preclimacteric, climacteric and postclimacteric stages, respectively. Treatmentof fruit with propylene, an analog of ethylene, decreased the firmness and enhanced the accumulation ofMA-XET1 transcript in the peel and pulp. These results suggest that MA-XET1 is involved in softening ofthe peel and pulp during banana fruit ripening and its expression is regulated by ethylene at transcriptionallevel.
文摘Radicle emergence and reserves mobilization are two distinct programmes that are thought to control germination. Both programs are influenced by abscissic acid （ABA） but how this hormone controls seed germination is still poorly known. Phenotypic and microscopic observations of the embryo axis of Medicago truncatula during germination in mitotic inhibition condition triggered by 10 μM oryzalin showed that cell division was not required to allow radicle emergence. A suppressive subtractive hybridization showed that more than 10% of up-regulated genes in the embryo axis encoded proteins related to cell-wall biosynthesis. The expression of α-expansins, pectin-esterase, xylogucan-endotransglycosidase, cellulose synthase, and extensins was monitored in the embryo axis of seeds germinated on water, constant and transitory ABA. These genes were overexpressed before completion of germination in the control and strongly inhibited by ABA. The expression was re-established in the ABA transitory-treatment after the seeds were transferred back on water and proceeded to germination. This proves these genes as contributors to the completion of germination and strengthen the idea that cell-wall loosening and remodeling in relation to cell expansion in the embryo axis is a determinant feature in germination. Our results also showed that ABA controls germination through the control of radicle emergence, namely by inhibiting cell-wall loosening and expansion.
基金supported by the National Natural Science Foundation of China (Grant No. 30901158)the Foundation for Key Program of Ministry of Edu-cation, China (Grant No. 104243)
文摘Xyloglucan endotransglycosylase is an identified relaxation factor with functions of easing and extending of plant cell walls.Its activities are directly related to plant growth and elongation of organisms.Anthocephalus chinensis is a tall and fast growing evergreen tree species.We cloned the full cDNA sequence of AcEXT genes which is abundantly expressed in the cambium of A.chinensis.The sequence analysis of nucleotides and amino acids revealed the presence of a 1396 bp full cDNA sequence,including a 960 bp complete open reading frame（ORF） encoding a 320 amino acid protein.The deduced amino acid sequence of AcXET was homologous to the other known XET proteins and contained the conserved EIDFE catalytic site which was specific to all the XETs.Our data should serve as a foundation for further insight into AcXET gene molecular mechanisms during wood formation and cell wall engineering of woody plants.
