| The roots system determines both the capacity of a sessile organism to acquire nutrientsand water, as well as providing a means to monitor the soil for a range of environmentalconditions to affect plant growth and development, which is very important for the wholeplants. The root apical meristem cells continued rapidly dividing, providing a steady stream ofnew cells for the plant roots and ultimately determines the final root architecture.Auxin is extensively involved in embryo development, root system development, apicaldominance, generative organ development and so on, which plays a crutial role in plantgrowth and development. Auxin can regulate the root apical meristem cell division, cellelongation and cell differentiation and so on. So there is a close relationship between auxinand root development. We screened a wali7domain containing protein ASR by microarraydata of auxin response analysis. In this paper, we investigated its expression pattern, functionand its mechanism of function in Arabidopsis. The results are as following:(1) We analyzed the expression pattern of ASR in Arabidopsis by qRT-PCR. The dataalso indicated that the expression level of ASR was higher in young shoots than that in roots.The ASR promoter::GUS analysis also showed strong GUS staining was observed incotyledons of3-day-old seedlings, while undetectable in root and GUS activities became lessand less weaker with the plant development. These results indicated that ASR was mainlyexpressed in cotyledons of young seedlings. The expression of ASR was induced when usingauxin to treat the WT and ASR promoter: GUS seedlings for different periods of time (6h,12h,24h). This result indicated that ASR is response to auxin and can be induced by auxin. And theresults of qRT-PCR indicated that ASR could also be induced by mannitol and AlCl3.(2) By analyzing the phenotype of ASR overexpresser, we found that ASR overexpressershowed short primary root phenotype during the whole development and showed delayedflowering. (3) Using microscope analysis, overexpression of ASR reduced the size of the meristemand elongation zone and the distance between root tip and the first root hair was shorter. Theactivity of the cell division was remarkably reduced in35S: ASR plants, which was indicatedby GUS reporter driven by the marker promter of CycB1;1. These results suggested thatoverexpression of ASR decreased the mitotic activity of root tip which resulted in the reducedroot meristem size.(4) By qRT-PCR analysis, we found that the expression level of PLT2in the35S: ASRroots was reduced to about40%of that of wild type. This result indicated that the inhibitedprimary root growth by overexpression of ASR was related to the depressed stem sell activityby down-regulated PLT2.(5) By GUS staining analysis, we detected the activity of GUS reporter driven by thesynthetic auxin response element DR5in the roots of35S: ASR plants. The result showed thatthe GUS activity was remarkably reduced in the roots of35S: ASR plants. The expressionlevels of TAA1and YUCCA2, two genes that contribute to the local auxin biosynthesis, werealso reduced in the35S: ASR root tips compared with that of the wild type. But the polarauxin transporter PINs, such as PIN1, PIN2, PIN7were not. These results indicated thatoverexpression of ASR could related to the inhibition of local auxin biosynthesis in the root.(6) We then further treated the35S: ASR#10and wild-type seedlings with IAA or NAA.NAA treatment inhibited the primary root elongation in wild-type in a concentrationdependent manner, while35S: ASR#10roots showed no significant inhibition of the primaryroot elongation with NAA concentration over0.4μM IAA treatment caused similar responsesto the NAA. Besides, the flowering time and growth of35S: ASR plants were basically inaccordance with those of the wild-type by low concentration of NAA treatment. These resultsfurther suggested that overexpression of ASR was associated with the auxin reduction in roottips. |
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