| Phosphorus is an essential nutrient element during plant growth and development.Phosphorus deficiency affects rice growth and reduces rice yield.Strigolactone is a novel plant hormone,which can regulate root growth,tillering and abiotic stress.P deficiency stress stimulates the synthesis and secretion of strigolactone of plant roots,thereby changing roots morphology and the process of phosphorus absorpting and transporting.OsRGAl is the a subunit of G protein in rice,studies have shown that OsRGAl is involved in the response of rice to low phosphorus stress and the regulation of plant growth by strigolactone,but the role of OsRGAl in the strigolactone regulating rice response to low phosphorus stress remains unclear.Therefore,further study about the effect of OsRGA1 on strigolactone regulating rice response to low phosphorus stress and its mechanism is of great significance,because it can reveal the function of OsRGAl and improve phosphorus use efficiency in rice.In this study,we used wild-type NIP,OsRGA1 mutant lines R-5 and R-8,and OsRGA1 overexpression lines ROE1 and ROE2 as materials.Through hydroponic and pot-culturing experiments,we set up the combination treatments of low phosphorus and strigolactone to observe the phenotypes of rice,determine the physiological and morphological indices,the content of strigolactone,the expression level of genes.So that we can investigate the role of OsRGAl in strigolactone regulating rice response to low phosphorus stress and its physiological and molecular mechanisms.The main results are as follows:1.In this study,two stable OsRGAl deletion mutants R-5 and R-8 and overexpression lines ROE1 and ROE2 were obtained from japonica rice Nipponbare(NIP).The relative expression level of OsRGAl in ROE1 and ROE2 increased by 2.34 times and 4.01 times,respectively.The results of western blot showed that OsRGAl protein bands were not observed in the mutants,but in both the wild type and overexpression lines OsRGAl protein bands were clear and the expression level of them were significantly higher than that of wild type.2.Using Normal phosphorus concentration(NP,300 μM KH2PO4)as control,We set up four low phosphorus treatments.Compared with NP,low phosphorus stress significantly increased the expression of OsRGA1 in NIP leaves.With the decreasing of P concentration,the relative expression of OsRGA1 firstly increased and then decreased.When P concentration was 1/60P(5 μM),the expression of OsRGA1 reached the maximum.Meanwhile,the content of strigolactone significantly increased by 183.22%.3.Low phosphorus stress promoted the longest roots elongation of various genotypes rice.Compared with NP,the length of the longest roots of NIP,R-5,R-8,ROE1 and ROE2 increased by 46.18%,23.73%,21.14%,48.98%and 56,14%under low P stress.The activities of antioxidant enzymes,acid phosphatase and the expression of phosphorus transporting genes were significantly increased,while the activity of roots was significantly decreased.The changes of the above indexes in ROE2 were greater than those in NIP,and in R-5 and R-8 were smaller than those in NIP.These results indicated that OsRGAl positively regulated rice the longest root elongation process promoting by low P stress.4.OsRGA1 affects the synthesis of endogenous Strigolactone(SL).Compared with NIP,the content of SL was significantly increased by 9.62%in ROE2 and decreased by 21.15%and 20.52%in R-5 and R-8.Exogenous strigolactone(GR24)treatment promoted the elongation of rice the longest roots.Compared with control,after the treatment of GR24,the length of the longest roots of NIP,R-5,R-8,ROE1 and ROE2 significantly increased by 54.76%,24.10%,20.07%,59.06%and 61.81%.The increase of expression of strigolactone synthesis genes(OsD10、OsD17、OsD27)in ROE2 were greater than those in NIP,but smaller in R-5 and R-8 than those in NIP.There was no significant difference in the increase of genes expression about strigolactone signal transduction among various genotypes rice.After inhibiting endogenous strigolactone synthesis(Tis108),the promoting effect of GR24 treatment on the longest roots elongation was decreased.These results indicated that OsRGA1 regulated the synthesis of strigolactone and was involved in the promoting effect of strigolactone on the elongation of rice the longest roots.5.After the treatments of low phosphorus stress and GR24,the length of the longest roots of NIP,R-5,R-8,ROE1 and ROE2 increased significantly by 26.13%,14.90%,16.76%,27.56%and 27.37%.The activity of roots,the activities of antioxidant enzymes and acid phosphatase,strigolactone content and the expression of genes about phosphorus transporting and strigolactone synthesis significantly increased.The changes of the above indexes in ROE2 were greater than those in NIP,and in R-5 and R-8 were less than those in NIP.Therefore,OsRGA1 positively regulated the response of strigolactone to low phosphorus stress.6.Compared with NP,under the condition of no phosphorus application,the number of panicle and seed setting rate of various genotypes rice were significantly decreased,the number of grains per panicle and 1000-grain weight were not significantly affected,and the yield was significantly decreased.OsRGA1 deficiency significantly decreased the agronomic phosphorus use efficiency,absorption use efficiency and partial phosphorus productivity,and decreased the seed setting rate and 1000-grain weight,and ultimately led to the decrease of rice yield,Strigolactone increased phosphorus use efficiency and seed setting rate,but decreased the number of panicle,and had no significant effect on the yield.In conclusion,the effects and mechanisms of OsRGAl in strigolactone regulating rice response to low phosphorus stress were systematically studied.It was determined that strigolactone promoted the the longest roots elongation of rice seedlings by increasing the activity of roots,activities of antioxidant enzymes and acid phosphatase,strigolactone content,the expression of genes about phosphorus transporting and strigolactone synthesis under low phosphorus stress.OsRGAl positively regulated strigolactone synthesis and participated in the process of strigolactone response to low phosphorus stress. |
