| The root system is a very important part of higher plants organs and it performs essential functions during plant development, including anchoring plants, uptaking water and nutrient, and responsing to environmental factors. Shaping root development could directly affect the status of plant growth condition, and thus the study of root developmen is also crucial in agricultural production. So studying root development not only has theoretical values, but also has practical significances.Auxin represents a key regulator of root development in higher plants. Recently, studies in modle plant Aribidopsis has revealed that there is a gradient distribution of auxin in root, which determines the fate of root development. The maintenance of the concentration gradient depends not only on the biosynthesis and metabolism of auxin, but more importantly on the polar transport of auxin. Auxin polar transport is achieved via membrane-bound influx carriers and efflux carriers, whose asymmetric localization on the cell membrane generates the directional net flux through the tissues. And the efflux carriers are considered to be more important in polar auxin transport. PIN proteins are members of the major efflux facilitator family of integral membrane proteins, which is composed of eight members in Aribidopsis. Each member of the PIN family displays a unique tissue-specific expression pattern and polar localization on cell membrane, which are determined by their specific sequences or promoters. The expression pattern and membrane loclizaton can be changed rapidly by stimulation of development and environment signals, thus the auxin flux will be changed.Cytokinin also plays an important role in root development. Latest study reveals that cytokinin regulates the expression of PIN proteins in root tip, thus regulates auxin polar transport. The balance between auxin and cytokinin is considered as the key factor which determines root develepment.Here, we study the function of AtRREl in details with the overexpression and loss function mutants. Results suggest that AtRREl could regulate root development in Arabidopsis by affecting auxin transport in a cytokinin related pathway. So the study of AtRREl reveals a crosstalk between auxin and cytokinin during root development.The main study results are described as follows:1. Study of overexpression and loss-function mutants suggests that AtRRE1is a negative regulator of primary root elongation. And the expression level of AtRREl directly contorts the differentiation rate in root apical meristem cells.2. Auxin plays key roles in root development, so we analyse the auxin concentration gradient in mutants background by analysing an auxin-report line1AA2::GUS, and the results reveals that overexpression of AtRRE1destroies the auxin gradient pattern in root tip.3. Analysis of the effects of exogenously applied auxins (IAA and2,4-D) on roots of WT and mutants grown on the inductive medium suggests that auxin response is not affected in overxpression or knockout of. However, IAA but not2,4-D, shows a stronger effect on WT than on AtRRE1overxpression mutant, indicating that auxin efflux, but not influx, is attenuated by inducible overexpression of AtRREl.4. Report lines are used to detect auxin transport carriers in mutants background and the results suggests that AtRRE1regulates auxin transport via controling the expression of PIN proteins.5. RT-PCR analysis reveals that induction of AtRREl expression could induce the expression of cytokinin response transcription factors ARR1and ARR12which are reported play critical roles in regulating auxin transport and root development. By analyzing the phenotype of rrel arrl arr12triple mutant, we consider that AtRE1’s function on root elongation depending on ARR1and ARR12. Thus our work on AtRRE1proposes a feedback loop in auxin and cytokinin interaction in controlling root cell division and cell differentiation... |
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