| Rice is one of the important food crops for humans,and its yield is usually has a closely association with the agronomic traits such as plant height and tillering.The major factors determining the plant height and tillering of rice usually include endogenous hormones and the environment.Endogenous hormones are mainly represented by gibberellin(GA),brassinolide(BR)and strigolactone(SL),in which gibberellin regulates plant height by promoting the cell elongation.However,the regulatory mechanism of gibberellin in rice tiller has not been specifically elaborated.In this study,a semi-dwarf mutant was isolated in the tissue culture experiment and named sd13.The mutant showed similar symptoms,like plant height and dwarf,including panicles,ear hair loss,increased tillering,and low seed setting rate,caused by the lack of endogenous hormones(such as GA and BR).The microscopic observation indicated that the cell elongation of the sd13 was impeded,while the endogenous hormones determining the cell elongation in rice are mainly GA and BR.In our study,the sd13 mutant treated by exogenous GA and BR revealed highly sensitive to these two hormones.However,only the mutant exposed to GA could be obviously restored.Furthermore,the sd13 did not display typical symptoms of BR deficiency,such as erect leaf blade and small leaf angle,implying that sd13 may be a GA-deficient mutant.To explore the molecular mechanism of mutant dwarfing,the sd13 was subjected to transcriptome sequencing.The results showed that the mutant exhibits a total of 631 of the differential expressed genes compared to the wild type(WT).We screened the differential expressed genes and found a gene,OsGA13 ox,which confirmed to be related with GA synthesis and up-regulated in the mutant while down-regulated after GA application.The qRT-PCR revealed that OsGA13 ox was significantly up-regulated in the stems and leaves of the mutant compared with the WT,and also up-regulated in the flowers,but there is no significant difference.The OsGA13 ox is a key enzyme participating in GA synthesis,which is responsible for the conversion of GA12 to GA53,while GA12 and GA53 are converted to GA4 and GA1,respectively.The activity of the GA4 is higher than GA1,and thereby suggested that the sd13 mutant might result from the decrease of GA4 synthesis.The results of the GA detection showed that compared with the WT,the GA4 content in the mutant was significantly reduced,and the GA1 content increased while the difference was not significant,demonstrating that the decrease of GA4 content is the major reason for the phenotype abnormality of the sd13.The sd13 mutant showed a semi-dwarf rather than a dwarf phenotype since the GA1 content in the mutant was determined to be within the normal range,indicating that the mutated gene in the mutant is not a synthetic upstream gene of the GA12,therefore,the downstream genes of the GA12 synthesis related genes,OsGA20 ox and OsGA3 ox,should be specially amplified and sequenced.The results showed that three OsGA20 ox genes and two OsGA3 ox genes in the sd13 have no base mutagenesis,suggesting that the content decrease of the GA4 in the mutant was triggered by the abnormal expression of the OsGA13 ox gene.Additionally,this study also found that GA can inhibit rice tillering.Venn diagram showed that a total of 12 of the differential expressed genes are co-expressed in both the WT and the sd13,in which the D14 gene is a specific receptor of SL having inhibition role in rice tillering.The qRT-PCR results demonstrated that the D14 gene in the mutant was down-regulated,but up-regulated in both WT and the sd13 after spraying GA3.Down-regulation of the D14 gene will alleviate the signal of SL which can promote rice tiller.The statistical data showed that the sd13 mutant increased significantly effective tiller number,while both the WT and the sd13 obviously decreased effective tiller number after spraying GA3,suggesting that enrichment profile of GA in rice regulates rice tiller by regulating the expression of the D14 gene. |
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