We report here that ORS1, a previously uncharacterized member of the NAC transcription factor family, controls leaf senescence in Arabidopsis thaliana. Overexpression of ORS1 accelerates senescence in transgenic plant...We report here that ORS1, a previously uncharacterized member of the NAC transcription factor family, controls leaf senescence in Arabidopsis thaliana. Overexpression of ORS1 accelerates senescence in transgenic plants, whereas its inhibition delays it. Genes acting downstream of ORS1 were identified by global expression analysis using transgenic plants producing dexamethasone-inducible ORSl-GR fusion protein. Of the 42 up-regulated genes, 30 （-70%） were pre- viously shown to be up-regulated during age-dependent senescence, We also observed that 32 （-76%） of the ORSl-dependent genes were induced by long-term （4 d）, but not short-term （6 h） salinity stress （150 mM NaCI）. Furthermore, expression of 16 and 24 genes, respectively, was induced after 1 and 5 h of treatment with hydrogen peroxide （H2O2）, a reactive oxygen species known to accumulate during salinity stress. ORS1 itself was found to be rapidly and strongly induced by H2O2 treatment in both leaves and roots. Using in vitro binding site selection, we determined the preferred binding motif of ORS1 and found it to be present in half of the ORSl-dependent genes. ORS1 is a paralog of ORE1/ ANACO92/AtNAC2, a previously reported regulator of leaf senescence. Phylogenetic footprinting revealed evolutionary conservation of the ORS1 and ORE1 promoter sequences in different Brassicaceae species, indicating strong positive selection acting on both genes. We conclude that ORS1, similarly to ORE1, triggers expression of senescence-associated genes through a regulatory network that may involve cross-talk with saltand H2O2-dependent signaling pathways.展开更多
Development of the functional endodermis of Arabidopsis thaliana roots is controlled, in part, by GRAS transcription factors, namely SHORT-ROOT （SHR）, SCARECROW （SCR）, and SCARECROW-LIKE 23 （SCL23）. Recently, it...Development of the functional endodermis of Arabidopsis thaliana roots is controlled, in part, by GRAS transcription factors, namely SHORT-ROOT （SHR）, SCARECROW （SCR）, and SCARECROW-LIKE 23 （SCL23）. Recently, it has been shown that the SHR-SCR-SCL23 regulatory module is also essential for spec- ification of the endodermis （known as the bundle sheath） in leaves. Nevertheless, compared with what is known about the role of the SHR-SCR-SCL23 regulatory network in roots, the molecular interactions of SHR, SCR, and SCL23 are much less understood in shoots. Here, we show that SHR forms protein com- plexes with SCL23 to regulate transcription of SCL23 in shoots, similar to the regulation mode of SCR expression. Our results indicate that SHR acts as master regulator to directly activate the expression of SCR and SCL23. In the SHR-SCR-SCL23 network, we found a previously uncharacterized negative feed- back loop whereby SCL23 modulates SHR levels. Through molecular, genetic, physiological, and morpho- logical analyses, we also reveal that the SHR-SCR-SCL23 module plays a key role in the formation of the endodermis （known as the starch sheath） in hypocotyls. Taken together, our results provide new insights into the regulatory role of the SHR-SCR-SCL23 network in the endodermis development in both roots and shoots.展开更多
文摘We report here that ORS1, a previously uncharacterized member of the NAC transcription factor family, controls leaf senescence in Arabidopsis thaliana. Overexpression of ORS1 accelerates senescence in transgenic plants, whereas its inhibition delays it. Genes acting downstream of ORS1 were identified by global expression analysis using transgenic plants producing dexamethasone-inducible ORSl-GR fusion protein. Of the 42 up-regulated genes, 30 （-70%） were pre- viously shown to be up-regulated during age-dependent senescence, We also observed that 32 （-76%） of the ORSl-dependent genes were induced by long-term （4 d）, but not short-term （6 h） salinity stress （150 mM NaCI）. Furthermore, expression of 16 and 24 genes, respectively, was induced after 1 and 5 h of treatment with hydrogen peroxide （H2O2）, a reactive oxygen species known to accumulate during salinity stress. ORS1 itself was found to be rapidly and strongly induced by H2O2 treatment in both leaves and roots. Using in vitro binding site selection, we determined the preferred binding motif of ORS1 and found it to be present in half of the ORSl-dependent genes. ORS1 is a paralog of ORE1/ ANACO92/AtNAC2, a previously reported regulator of leaf senescence. Phylogenetic footprinting revealed evolutionary conservation of the ORS1 and ORE1 promoter sequences in different Brassicaceae species, indicating strong positive selection acting on both genes. We conclude that ORS1, similarly to ORE1, triggers expression of senescence-associated genes through a regulatory network that may involve cross-talk with saltand H2O2-dependent signaling pathways.
文摘Development of the functional endodermis of Arabidopsis thaliana roots is controlled, in part, by GRAS transcription factors, namely SHORT-ROOT （SHR）, SCARECROW （SCR）, and SCARECROW-LIKE 23 （SCL23）. Recently, it has been shown that the SHR-SCR-SCL23 regulatory module is also essential for spec- ification of the endodermis （known as the bundle sheath） in leaves. Nevertheless, compared with what is known about the role of the SHR-SCR-SCL23 regulatory network in roots, the molecular interactions of SHR, SCR, and SCL23 are much less understood in shoots. Here, we show that SHR forms protein com- plexes with SCL23 to regulate transcription of SCL23 in shoots, similar to the regulation mode of SCR expression. Our results indicate that SHR acts as master regulator to directly activate the expression of SCR and SCL23. In the SHR-SCR-SCL23 network, we found a previously uncharacterized negative feed- back loop whereby SCL23 modulates SHR levels. Through molecular, genetic, physiological, and morpho- logical analyses, we also reveal that the SHR-SCR-SCL23 module plays a key role in the formation of the endodermis （known as the starch sheath） in hypocotyls. Taken together, our results provide new insights into the regulatory role of the SHR-SCR-SCL23 network in the endodermis development in both roots and shoots.
