| The GRAS gene family is an important plantspecific gene family of putative transcription factors.In the past few years,researchers have reported evolutionary analyses based on the genome-wide comparisons of GRAS family members among 17 representative species.In 14 species,a total of 837 GRAS proteins were identified.The GRAS gene family encodes transcriptional regulators that have diverse functions in plant growth and development,such as gibberellin signal transduction,phytochrome A signal transduction,axillary meristem initiation,radial organization of the root,shoot meristem maintenance,and male gametogenesis.Compared with other families of transcription factors,very few researches have explored the whole genome of the GRAS family.To date,only 33,57,48,and 46 GRAS proteins were identified in the whole genome of Arabidopsis,rice,Chinese cabbage and Prunus mume,respectively.Due to the practical value of maize and its scientific value is higher and higher,we choose maize as the material of our research.As the whole genome sequences have been gotten of the B73 ecotype in 2009,makes our researches practicable.But due to the maize genome is too large and very complex,transformation of maize is still quite difficult for us,so we choose the Arabidopsis thaliana and Brachypodium distachyon as modles to study the function of the maize GRAS genes,the results are as follows:(1)We got 92 GRAS transcription factor members in maize B73 ecotype,most of them contain one or more conserved motif in GRAS family-the GRAS motif in the C terminal.GRAS family genes possess the five carboxy-terminal motifs that are characteristic of the GRAS family.In order these include: leucine heptad repeat ?,the VHIID motif,leucine heptad repeat ?,the PFYRE motif,and the SAW motif.(2)To study the evolutionary history and the relationships of GRAS transcription factors in maize,the GRAS proteins from other two model plants,Arabidopsis and rice,as well as the most familiar specie Sorghum bicolor were performed for analyzing and comparing.The phylogenetic analysis indicated that 92 GRAS proteins can be divided into 8 subfamilies according to the clade support values,topology of the tree,and classification of Arabidopsis,designated as clade I to VIII named SCL3,HAM,SCR,DELLA,SHR,PAT1 and LISCL.Besides the conserved domain in the C terminal,most of the DELLA subfamily members have a conserved domain in the N termimal named DELLA domain,while the LISCL members also have some domains conserved in the N terminal.(3)All the 92 Zm GRAS genes distributes on all the 10 chromosomes in maize randomly.The number of the genes in different chromosomes varies not so much,besides there are only 3 members on No.8 chromosome.Among all the genes,there are ten pairs of orthologous genes,which mean that there were tandem duplications occurred before.Among the ten pairs of orthologous genes,there are three pairs of them clustered together on different chromosomes.This phenomenon may dues to segmental duplication.Because all the genes were very conservative along the evolution,the genes still look the same after the duplication.(4)We analyzed the expression patterns of the 92 Zm GRAS genes,and found that their expression patterns differed a lot.The expression patterns can be divided into 6 clades,each clade members' expression patterns in different tissues are familiar.We got materials from different tissues and the q RT-PCR results made the data believable.(5)We cloned most of the Zm GRAS genes and constructed expression vectors to observe whether there is something abnormal in the overexpression plants.Over-expressed Zm GRAS47 and Zm GRAS84 in Brachypodium distachyon resulted different levels of dwarf phenomenon,while in the transgenic Arabidopsis plants of Zm GRAS84 there is no obvious difference compared with the widetype.Over-expressed Zm GRAS41 and Zm GRAS74 in Arabidopsis showed elongated hypocotyls,and Over-expressed Zm GRAS39 and Zm GRAS40 in Arabidopsis made the transgenic plants flowering earlier than the widetype. |
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