Functional Study Of Tomato Transcription Factor Genes SlJAZ2 And SlAGL6 In Flower Development

Flowering is an important event in the life history of angiosperms and it is also a significant indication of the transition from vegetative growth to reproductive growth.After the growth of plants reaching a certain stage,the transition to vegetative growth begins under the combined action of various factors.After a series of complex processes,the construction of floral organ is complished.As an important model plant used for the study of reproductive growth and fruit ripening,and a vegetable crop as well,the regulation of flower development and flowering time is closely related to the yield and early maturity breeding of tomato.In recent years,we have known about the regulation of flowering time by the studies on flower development related genes.However,the existing mechanism of flowering time regulation is still not completely illuminated.The members of JAZ family are inhibitors in jasmonate pathway.The existing reports reveal that JAZs play vital roles in response to biotic,abiotic stresses and hormones.Furthermore,they participate in multiple processes of plant vegetative and reproductive growth.In Arabidopsis,At JAZ1 plays an important role in the regulation of flowering time by modulating the expression of FT,a key gene in flowering regulating pathway.In order to further explore the the roles of tomato JAZs play in regulating flowering time,we cloned Sl JAZ2 gene.Expression pattern analysis revealed that Sl JAZ2 massively distributed in flower which indicated its possible role in tomato flowering process.Sl JAZ2 was over-expressed in wild-type tomato by vector construction and Agrobacterium mediated transformation.We found that leaf initiation in transgenic plants were faster than wild-type plants.The plant height and internode length of transgenic tomato plants were reduced compared to wild-type.Further anatomical analysis showed that the cells in stem of transgenic plants were decreased in size.In addition,the expression of cell elongation and gibberellin biosynthesis related genes were inhibited.After overexpressing Sl JAZ2,the trichomes on stem epidermis were less than wild-type and the lateral buds initiated earlier and more exuberant than wild-type,and detection of genes related to trichome and lateral buds development agreed with the phenotypes.The flower buds initiated about one week earlier than wild-type and the detection of genes related to flowering showed that the expression of FA,UF and SFT were all affected in Sl JAZ2 over-expression transgenic tomato plant.What’s more,the expression of three AP2 family genes which probably function in the upstream of SFT were also siginificantly inhibited.These results showed that Sl JAZ2 participated in both the plant morphogenesis at early stage and flowering time which lay the foundation for further exploring the regulatory network and molecular mechanisms of flowering time in tomato.MADS-box is a transcription factor gene involved in plant reproductive growth.AGL6 is a subfamily of MADS-box and the members have been reported participating in modulating flowering time by regulating FT and other genes regulating flowering time in Arabidopsis.In other species,AGL6 can also regulate the development of floral organs.In this study,we identified the only member of tomato AGL6 lineage,Sl AGL6,and the expression analysis showed that Sl AGL6 specifically expressed in flower which indicated that Sl AGL6 probably participated in tomato flowering.Furthermore,the expression profile of Sl AGL6 in four floral organs revealed the highest transcript level appeared in petals and carpels,followed by sepals,and the lowest in stamens.These results indicated the possibility of Sl AGL6 in participating in the development of petals,carpels and probably in sepals.We obtained Sl AGL6-silenced transgenic tomato plants by RNAi technology and Agrobacterium mediated transformation.We observed that the transgenic plants produced fused sepals and green petals.Gene expression analysis results showed that genes related to sepal development(MC,AP2 a,AP2c)and boundary establishment(GOBLET)were down-regulated in transgenic lines.In transgenic petals,the chlorophyll content was higher than wild-type and two chlorophyll synthesis genes(Sl GLK1,Sl GLK2),two photosystem-related genes(Slrbc S3 B,Sl Cab-7)were induced and three B-class genes TM6,TAP3 and Sl GLO1 were repressed.These results suggested that Sl AGL6 was involved in petal development by affecting the expression of B-class genes.In addition,detection of other genes participating in floral organ development showed that the expression of C-,D-and E-class genes were all influenced in transgenic plants.Taken together,Sl AGL6 involves in tomato sepal and petal development and these results lay foundation for the study of AGL6 lineage evolution and gene functional division in different species.In summary,our study explored the function of two transcription factor genes possibly affecting the flowering time in tomato.We found that the jasmonic acid pathway inhibitor gene Sl JAZ2 played a role in regulating plant morphogenesis and flowering time in tomato.However,Sl AGL6 had no significant effect on the flowering time of tomato,but it was involved in the morphogenesis of floral organs.These results lay foundation for illuminating the regulatory mechanism of flowering time and floral organ morphogenesis.