Functional Analysis Of DiASR1 Which Is Superior Expression Gene In Dove Tree Bracts

Dove tree is a rare and endangered tree species.It is endemic to China and has been listed as the first degree national protective plant.The spherical inflorescences with opposite leaf-shaped large bracts at the base in dove tree look like dovesperching on the tree,which is the origin of its name.Dove tree is an ornamental plant with very high praise,mainly due to its showy bracts.Bract is a kind of metamorphic leaf.According to the morphological features,the development process of bract could be divided into four stages,including green young bract,light green young bract,white unfolded bract and yellow wilting bract.In order to reveal the regulatory mechanism of bract development in dove tree,we performed transcriptome analysis in bract and leaf.Based on the transcriptome data,we identified an ASR homologous gene with preferential expression in bracts The full-length sequence of the ASR homologou gene was cloned and named as DiASR1.We analyzed the expression pattern of DiASR1 in different tissues and during the developmental stages of bract.The function of DiASRl was validated in in Arabidopsis and tobacco,respectively,by overexpression On the other hand,in order to analyze the regulation mode of DiASR1,its upstream promoter sequence was cloned,and an expression vector containing the promoter of DiASRl and GUS reporter gene was constructed and transformed into.Arabidopsis thaliana.GUS expression under different organs and different stress conditions was observed by histochemical staining.The results of this study are shown as follows:1.DiASR1 was identified to be a member of the ASR gene family,but it has low homology with the known ASR gene sequence in other species.2.The expression of DiASR1 gene gradually increased during the development of bracts.Furthermore,the expression level of DiASRl has a significant positive correlation with the area of bracts,which suggesting that DiASR1 might play an important role in the growth of bracts.In the later developmental stage,the expression levels of DiASR1 in the small bracts was significantly higher than that in the large bracts,suggesting that DiASR1 may also be involved in asymmetric development of the bracts.3.Phenotypic observation of the transgenic plants of Arabidopsis and tobacco revealed that DiASR1 can shift vegetative growth into reproductive growth earlier intransgenic plants.In transgenic plants,the number of inflorescences of increased,and the number of leaves decreased.Additionally,DiASRl also caused albino leaves in Arabidopsis,and altered the petal color from red to light white in tobacco.These results suggested that DiASR1 might inhibit the pigment synthesis.4.Under the high salt stress,transgenic lines showed lower survival rates.The root length of the transgenic plants was shorter than that of wild type seedlings.Transgenic lines were more sensitive to salt stress and showed a lower tolerance.The results indicated that overexpression of DiASR1 gene could reduce the adaptability of Arabidopsis plants to salt stress.5.A 500 bp promoter fragment of DiASRl gene was cloned and named as PDiASR1.The cis-elements in PDiASR1 was analyzed and cis-elements involved in response to light,heat and other abiotic stress were found,indicating that the promoter may be regulated by light and temperature conditions.GUS histochemical staining showed that the expression level of PDiASR1 was high in organs with strong division,such as young leaves,stamens and branches.After treatment in high salt,drought and dark conditions,the expression level of GUS decreased,suggesting that the expression of PDiASR1 was negatively regulated by stress.Our results indicate that the DiASRl gene from dove tree can regulate the reproductive development of plants,shift plants from vegetative growth into reproductive growth,and cause a certain degree of albino tissues in different parts.Differently,the overexpression of DiASRl gene reduced the salt tolerance of Arabidopsis plants,suggesting that the dove tree ASR gene was functionally specific.DiASRl gene is specifically expressed in the bracts of dove tree,and its expression is positively correlated with the area of bracts.It may participate in the development of bracts by inducing chloroplast degeneration and reducing the resistance capability to environmental stresses.