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Mechanisms Of Brassinosteroid Promotion On Tropisms And Root Development Through Regulating Polar Auxin Transport In Dicotyledonous Plants

Posted on:2007-10-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:L LiFull Text:PDF
GTID:1100360185456817Subject:Molecular genetics
Abstract/Summary:PDF Full Text Request
Plant hormone BRs (Brassinosteroids) act as important players in plantmorphogenesis. Previous studies indicated that BR treatment enhanced auxin-relatedresponses (Mandava et al., 1988), but the underlying mechanisms remain unknownBy using 14C labeled IAA and Arabidopsis thaliana plants harboring an auxinresponsive reporter construct (DR5-GUS), we show that the BR stimulates polar auxintransport (PAT) capacities and modifies the distribution of endogenous auxin. Whileexogenous BR does not affect the overall levels of endogenous IAA, it does influence theaccumulation of auxin in different tissues. The expressions of PIN gene family werestudied by real-time PCR in detail and the results showed that PIN genes were regulatedunder BR treatment, indicating that effects of BR on plant development such as hypocotylelongation, root growth or tropistic responses, may be mediated by a general impact of BRon the expression of PIN genes.For the first time, we proved BR modulation on tropisms in dicotyledonous plants.Studies on the localization of PIN2 from the root tip up to the elongation zone, as definedduring the tropistic processes, indicate the BR regulation on its accumulation. In addition,the polar localization in meristem cells of root tip and expression of ROP2 in elongationzone are induced by gravity, and affect PIN2 expression and localization. Analysis on therelative mutants and transgenic plants reveals that BR first affects ROP2 expression,localization and activity, thereby modulates expression and localization of PIN2, the latterbeing modulated by F-actin-dependent processes.BR promotes lateral root development, which has been proved closely connected withpolar auxin transport (PAT) activities in root (Bao et al., 2004). Our further researchdisplays the hormones effects on root formation, and it's revealed that BR induces rootorgans in hypocotyls of plant seedlings. And one transcription factor SCARECROW(SCR)-controlled asymmetrical cell division may play a key role in its underlyingregulating pathways.The data presented in this report provide results of BR-modified plant developmentbased on the systemic research. For the first time, the regulation of one plant hormone BRon auxin to modulate plant morphogenesis has been confirmed, which give us cues to dofurther research on such "net-work" between distinct signal pathways. And the key factorsunderlying the physiological effects and mechanisms of plant hormones have been foundout and discussed their functions during the responses, which encourages us to develop thefunctional characterization of plant hormones.
Keywords/Search Tags:BR, polar auxin transport, G protein, transcription factor SCR, plant morphogenesis
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