Study On The Regulation Of Abscisic Acid In Primary Root And Shoot Growth Of Rice Seedling

Abscisic acid?ABA?is an important plant hormone and plays an essential role in the plant growth and development regulation and stress responses.ABA is involved in many plant growth and development processes including seed dormancy,germination and maturation,stomatal closure,leaf senescence,fruit maturation,root structure,seedling growth and vegetative growth.However,the molecular basis of ABA regulation in rice growth is unclear.Studies have shown that ABA regulates primary root growth by auxin,ethylene,reactive oxygen species and Ca²⁺in Arabidopsis.In this study,yucasin?an activity inhibitor of YUCCA,a key enzyme in the auxin synthesis pathway?and ABA were applied to treat rice seedling at the same time and it was found that yucasin could relieve the inhibition of primary root elongation by ABA,indicating that the inhibition of primary root elongation by ABA was dependent on the activity of YUCCA.qPCR assay was performed to detect the expression of OsYUCCAs?OsYUCs?genes in the primary root after ABA treatment,and the results showed that ABA induced the expression of the auxin biosynthetic genes OsYUCs.Furthermore,GUS staining assay showed that ABA promoted the auxin accumulation in rice roots.In order to further explore the role of YUCCA in the inhibition of primary root elongation by ABA,we tested the responses to ABA of the osyuc mutants,and found that osyuc8 mutant was more insensitive to ABA,indicating that ABA could regulate primary root elongation in rice through OsYUC8.The transient expression experiment in protoplasts also showed that ABA could induce the expression of OsYUC8 gene.Promoter analysis showed that OsYUC8 promoter contained binding elements of OsbZIP.Furthermore,after ABA treatment OsbZIP46 overexpression lines were more sensitive to ABA,while osbzip46 mutant was more insensitive to ABA.The phenotype of osbzip46 mutant primary root was consistent with that of osyuc8 mutant.qPCR data showed that OsbZIP46 positively regulated the expression of OsYUC8 gene.The above results indicated that ABA might positively regulate the expression of OsYUC8 via OsbZIP46 to promote auxin biosynthesis and inhibit the primary root elongation.Gibberellic acid promotes the shoot growth of plant and antagonizes the inhibition effect of ABA.It was reported that the down-regulation of OsPK1 gene in rice?which encodes cytoplasmic pyruvate kinase?leads to the change of ABA/GA ratio and affects rice height.In this study,we found that gibberellic acid could relieve ABA inhibition of shoot growth.In addition,the gene chip data showed that ABA reduced the expression of gibberellin biosynthetic genes.In order to explore the relationship between ABA and gibberellin,qPCR assay was performed to detect the expression of key gibberellin biosynthetic genes after ABA treatment,the results showed that ABA could inhibit OsCPS1,OsKO2 and OsSHB genes expression.These results indicated that ABA could inhibit the shoot growth of seedlings by inhibiting the expression of gibberellin biosynthetic genes.In conclusion,in the rice seedling stage ABA inhibits primary root growth by promoting the auxin biosynthesis and ABA inhibits the seedlings shoot growth by inhibiting the gibberellin biosynthesis.This study provides a model for the regulation of root and shoot growth by the interaction between ABA and auxin/GA.