Cloning And Characterization Of Photoperiod Sensitive Gene ZmGI In Maize

Maize (Zea mays ssp. mays L)is an important crop, to ensure national food security plays a decisive role. Tropical and subtropical germplasms contain abundent hereditary variation to broaden Chinese maize germplasm and increase the breeding level., but the primary limiting factors from these sources when applied in a temperate zone is photoperiod sensitivity.Maize tropical zone inbred line CML288, which is highly sensitive to photoperiods, was obtained from the Mexico International Maize and Wheat Improvement Center (CIMMYT), The full-length cDNA of GIGANTEA of Zea mays (ZmGI) gene was isolated by RT-PCR and 5′and 3′RACE methods from CML288 We studied the expression of ZmGI in shoot apical meristem (SAM) and leaf under long day and short day conditions between 3-leaf and 8-leaf stages,and test its transcription level by Real-Time PCR during 24 hour. The main results are as follows.1. Isolation and sequence analysis of the ZmGI geneThe full-length cDNA of GIGANTEA of Zea mays (ZmGI) gene, which has extensive sequence homology to photoperiod genes GI in Arabidopsis, was isolated by RT-PCR and RACE methods. A 4156-bp full length cDNA sequence with a 14-bp polyA was obtained.The corresponding gene was named ZmGI, an ORF encoded predicted polypeptide of 1161 amino acids. Analysis shows that the 544-772 amino acid region in CML288 is the nuclear localization protein region, among which the nuclear localization signal GRSRCKKRQ is detected with a conservatism sequence, At the nucleotide and protein levels, ZmGI showed highest identity with OsGI. The construction homology tree conforms to the plant evolution relations. it was mapped in the chromosome 8.03.2. Expression of ZmGI gene over 24 h and from the 3rd to the 8th full expansion leafQRT-PCR shows ZmGI expression exhibits diurnal fluctuations in leaves. In LD, ZmGI expression began to slowly increase at 4-8 h after dawn, rapidly ascended with accumulated illumination to peak at approximately 12 h after dawn; In SD, ZmGI expression peaked approximately 8 h after dawn, and finally reached trough levels around dawn. In SAMs, ZmGI expression also showed certain cyclical features under LD and SD conditions.Under LD conditions, expression in the 3-8 leaf stages increased throughout. Under SD conditions, expression from the 3rd to 5th full expansion leaves increased gradually, and peaked at the 6th full expansion leaf; however, at the 7th full expansion leaf stage, ZmGI expression appeared to descend, and continued descending at the 8th full expansion leaf. The SAMs showed no visible difference between the 6th and the 8th full expansion leaves. Under SD conditions the SAM shape of leaf-period 6 did not have distinct variance and the SAM always differentiated into a leaf primordium. However, at the 7th full expansion leaf, the stem tips were already elongated and became conical, and an obvious cone phenotype was apparent in leaf-period 8.3. Got the overexpression Arabidopsis plant of ZmGI and its function analysisWe constructed the overexperssion veter PBI- ZmGI then transformed it into Arabidopsis with Floral Dip method,and got the transformant plant hd6-ox.It found that ZmGI -ox plants flowered earlier than wt about 16 d under LD condition. ZmGI -ox plants and wt flowered later than LD under SD condition,CO under LD conditions exhibited more expression both in ZmGI -ox plants than wt plants. ZmGI is suggested to function as a floral activator under inductive days.