The Mechanism Of Strigolactones Regulating Rice Root Growth And Development In Respone To Nitrogen And Phosphate Nutrition

Nitrogen(N)and phosphate(P)are major nutrients required for plant growth and development.N and P deficiencies dramatically affect plant development and crop productivity.Adaptation of root morphology in response to nutrient deficiencies would help plant to improve nutrient uptake.Therefore,ideal root morphology is the important physiological basis for nutrient uptake under nutrient deficencies.Root growth is regulated by environmental conditions and intrinsic factors(e.g.plant hormones).The plant hormone auxin(indole-3-acetic acid,IAA)is an essential regulator in plant.Many researches have shown that auxin polar transport is involved in the growth and development of plant root.In addition to auxin,strigolactone and their derivatives(SLs)have recently been defined as novel phytohormones to regulate root development.It have been demonstrated that N and P deficiencies significantly induced the exudation of SLs in nonleguminosae species.It remain obscure whether SLs was involved in root growth regulated by N-and P-deficiencies and the relation between SLs and auxin.Nitric oxide(NO)is a signalling molecule involved in the process during plant root development.But the mechanism of this process and the target of NO signaling remained unclear.In this study,we analyzed the exduation of SLs from the rice root under N-P-deficient conditions and the root development in wild type(WT),SLs sythesis mutants(d10 and d27)and signal mutant(d3)in response to N-and P-deficiencies and application GR24.Then,we analysed the relationship between SLs,auxin and NO during the root development regulated by N-and P-deficient conditions.The results were listed as follows.1.Rice d mutants with impaired SL biosynthesis and signalling exhibited reduced AR production compared to the wild type.Application of GR24 increased the number of AR and average AR number per tiller in d10,but not in d3.These results indicate that rice AR production is positively regulated by SLs.Higher endogenous IAA concentration,stronger expression of DR5::GUS and larger[3H]IAA activity were found in the d mutants.Exogenous GR24 application decreased the expression of DR5::GUS,likely indicating that SLs modulate AR formation by inhibiting polar auxin transport.The WT and the d10 and d3 mutants had similar expression of DR5::GUS regardless of exogenous application of NAA or NPA;however,AR number was greater in the WT compared to the d mutants.These results revealed that AR formation in rice regulated by SLs and auxin status,but the interaction between the SLs and auxin in regulating AR formation appears to be more complex.2.Reduced concentration of either P or N led to increased seminal root length and decreased lateral root density in WT.Limitation of either P or N stimulated SL production and enhanced expression of D10,D17 and D27 genes,and suppressed expression of D3 and D14 genes in WT roots.Mutation of D10,D27 or D3 gene caused loss of sensitivity of root response to P and N deficiency.Application of SL analog GR24 restored seminal root length and lateral root density in WT,d10 and d27 mutants but not in the d3 mutant,suggesting that SLs were induced by nutrient-limiting conditions and led to changes in rice root growth via the D3 gene.3,Compared with normal condition,auxin in rice root of WT was reduced under low-P and-N concentrations.P-or N-deficient conditions or GR24 application reduced the transport of[3H]IAA,the activity of DR5::GUS auxin reporter and the levels of most PIN family genes in WT,d10 and d27 mutants.These findings highlighted that SLs regulated the development of rice roots by modulating transport of auxin from shoots to roots.4.The NO-assoicated green flurescence in the root tip was visibly increased by LN and LP.The application of 10?M SNP significantly increased NO-associated green fluorescence in the root tips,and induced the seminal root length to the same extent as LP and LN.Application of the NO scavenger(cPTIO)under LN or LP decreased NO-associated green fluorescence in the root tips and also decreased the seminal root length to a similar level to the control treatment.LN and LP induced NO accumulation is need for seminal root elongation.NO induced by LN is NR and NOS dependent and NOS dependent under LP.Nia2 mutants are less sensitive to low N than low P.5.Similar NO accumulation was observed in the root tips of WT,d10 and d3 mutants regardless of the nutrient conditions,indicating that mutation of SL synthesis and signaling did not affect NO accumulation induced by LN and LP.No responses were observed in two SL d mutants compared to wild-type(WT)plants,in terms of root elongation after application of sodium nitroprusside(SNP),although similar NO accumulation was induced by SNP.Application of the SL inhibitor Abamine2+SNP reduced seminal root lengths and expression of pCYCB1;1::GUS induced by the application of SNP in WT plants,suggesting that NO acted upstream of SLs to induce root elongation in response to nutrient deficiencies.Western blot analysis and application of MG132(a proteasome inhibitor)revealed that NO,similar to SLs,triggered proteasome-mediated degradation of D53 protein levels(a repressor of SLs).This indicated a novel signaling pathway in which NO acted upstream of SLs to activate seminal root elongation under N-and P-deficient conditions in rice.In conclusion,elevated excudation of strigolactone was observed in WT plants inder N and P-limiting conditions relative to those under conditions of sufficient respective nutrient availability.Strigolactones regulated the development of rice roots via D3 component of SL signaling.While the interaction between the SLs,auxin and NO in regulating appears to be more complex in this process.