| Utilization of heterosis plays an important role in increasing crop yield,improving quality,and strengthening resistance.It has become one of the main ways for crop improvement.With the development of genomics and mordent molecular biology technology,we can identify genes associated with yield heterosis in maize,and analyze its’ function.This will help us to improve the level of heterosis utilization and yield in maize.With the rapid development of molecular biology techniques,the molecular breeding has contributed greatly to maize genetic breeding.Among them,the transgene technology can break the isolation between species,facilitate the transfer of genes between different species,and broaden the genetic source of crop genetic improvement.The application of transgene technology in maize breeding,can not only change the objective properties of corn on purpose and improve the selection efficiency of maize conventional breeding,but also enrich the basis of corn breeding materials.In previous studies,through the high-throughput differential gene expression profiling analysis,a large number of genes associated with heterosis have been identified.Subsequently,many genes associated with corn grain yield heterosis were defined by the Gene Ontology,and four functional genes were cloned and characterized.ZmMYBE1 showed higher expression level in immature ears.It showed higher expression level in superior hybrid C8605-2×W1445 than in inferior hybrid C8605-2×W245,and overdominant patterns among C8605-2×W1445 and its parental lines.The overexpression of ZmMYBE1 in Arabidopsis resulted in retard growth rate,lower plant height,and prolonged growth period.According the forementioned results,the present work focus on the genetic transformation of ZmMYBE1 in maize inbred lines,the main progress of this research are introduced as follows,1、Generating the over-expression construct of ZmMYBEl driven by the super CaMV 35S promoter.2、Utilizing Agrobacterium transformation by inoculating immature maize embryos,six positive transgenic plants were obtained and named with ZC-77,ZC-87,ZC-103,ZC-106,ZC-118 and ZC-119,respectively.3、The genotype of the transgenic plants at the T1 and T2 generation was characterized using PCR method.4、The results of quantitative real-time PCR showed that the expression level of ZmMYBE1 in the offspring of transgenic homozygous plants of ZC-77,ZC-103,ZC-118 were increased by 7～10 fold compared to the negative control plants.5、Near isogenic line were generated by crossing the selected transgenic plants with M54,PH4CV and zheng58 respectively.The yield of derivative hybrids will be tested in field.Throughout their life cycle,plants are subjected to various types of abiotic stresses,including salinity,water deficit,low temperature and so on.Salinity is a major abiotic stress in plant agriculture worldwide,causing negative effects on crop growth and productivity.Numerous researches have suggested that when exposed to stressful conditions,plants accumulate an array of metabolites,particularly amino acids.Among them,proline biosynthesis has been well studied and shown to play important roles in plant tolerance toward various abiotic stresses.It has long been recognized that the accumulation of the three BCAAs exhibited more significant change than proline in some cases of osmotic stresses,implying that BCAAs may play a role in plant stress responses.However,no functional evidence has been obtained to draw such a conclusion.In addition,plant life cycle alternates between a diploid sporophytic phase and a haploid gametophytic phase,and gametophytic development is essential for plant reproduction.Valine(Val),leucine(Leu)and isoleucine(Ile)are grouped as branched-chain amino acids(BCAAs),as they all contain small branched hydrocarbon residues.They all are essential amino acids,and are able to de novo synthesize in numerous organisms including bacteria,fungi and plants,but not animals.Dihydroxyacid dehydratase(DHAD)catalyses a key step in the BCAAs biosynthetic pathway.In Arabidopsis thaliana,DHAD is encoded by a single gene(AT3G23940),but,so far,its biological function in controlling plant development remains uncharacterized.In this study,we utilize the model plant Arabidopsis as our research materials,and obtained four different T-DNA insertion lines named dhad-1,dhad-2,dhad-3 and dhad-4 respectively.The insertions of dhad-1 and dhad-2 reside in the putative promoter or 5’UTR regions,the insertions of dhad-3 and dhad-4 locate in the first exon and the third intron of AtDHAD,respectively.Our research results are as follows,(1)In Arabidopsis thaliana,DHAD is highly expressed in most vegetative and reproductive tissues,(2)AtDHAD is an essential gene,and the complete disruption resulted in partial sterility in both male and female gametophyte,(3)Reduced expression of DHAD in knockdown mutants resulted in a reduction in the accumulation of all three BCAAs in roots and,as a consequence,led to a shorter root phenotype,which could be restored by an exogenous supplement of free isoleucine,(4)The knockdown mutants became hypersensitive to salt stress,not to heavy metal stress,and the high sensitivity to salt stress is quite specific,implying that BCAAs may act as osmotic protections in salt tolerance.This is the first time to provide strong evidences to suggest that BCAAs homeostasis has an important impact on plant salinity tolerance.And this would be the second amino acid shown to confer such a function in addition to the well-documented proline.In summary,our results provide evidence that BCAAs biosynthesis plays important roles in gametophyte and root development,and BCAAs homeostasis contributes to the adaptation of Arabidopsis to salinity stress. |
