Expression Of Photoperiod-related Genes During The Flower Induction And Reversion In Soybean

Soybean is a typical short-day plant,being considered as the model plant in the early studies of photoperiodism.Compared with other SD plants,like rice and maize,soybean is more sensitive to photoperiod and the difference among different cultivars is greater than that in rice and maize.The fact that different soybean cultivars can only be planted in limited area due to their sensitivity to photoperiod restricts the extensive cultivation of soybean.For late-maturing soybean,which is sensitive to photoperiod,short-day condition is not only necessary for flower induction,but for blooming, podding and seed maturation.The inapposite photoperiod may result in delayed reproductive phase or even back to vegetative growth.The understanding of photoperiod mechanism involved in soybean may benefit the breeding of extensively adapted soyeban cultivars.In the present study,four photoperiod-related genes were cloned in soybean using RACE,and seven homologues were obtained through BLAST search.Their expression patterns in our exprimental system,which is SD(blooming),LD(persistant vegetative growth),LD-SD(flower reversion),were detected using Real-Time PCR.To further detect the function of GmSOC1,a rapid and highly efficient transforamtion platform was established through Agrobacterium rhizogenes-mediated trnasformation of Lotus corniculatus.Transgenic GmSOC1 L.corniculatus was obtained and its function was investigated. The detailed results were mentioned as follows:1.Four photoperiod-related genes in soybean were cloned,named GmCOL1,GmCOL2,GmCOL3 and GmSOC1,corresponding to proteins of 311,365,310 and 211 amino acids,respectively.The putative amino acid sequence of GmCOL1,GmCOL2 and GmCOL3 showed high similarity with MsCO-like and PsCO-like;the putative amino acid sequence of GmSOC1 showed 70%similarity with AtAGL20,and is a member of MADS-box gene family.2.A suitable internal control makes gene expression results from Real-Time PCR more reliable. We performed a systematic study among ten selected housekeeping genes to validate the most suitable internal control in soybean by Real-time PCR.GmELF1B showed relatively constant expression pattern in the photoperiod response of soybean,and theffore was selected as an internal control in the gene expression studies of photoperiod in soybean.3.The expression patterns of 11 photoperiod-related genes were detected during the flower induction of ZGDD,a photoperiod sensitive cultivar.The results indicated that all of them were expressed under SD or LD conditions and the difference is that they were expressed in different abundance and following different rules.They were not specifically induced by SD condition and LD condition also induced their expression at a given stage.4.The expression patterns of the 11 genes were also detected in the SAM of cultivars with different sensitivity to photoperiod and they were all expressed in HH27,a non-sensitive cultivar and ZGDD,a sensitive cultivar.However,the expression peak in HH27 appeared earlier than that in ZGDD, which coincides with the earlier flowering phenotype of HH27 in SD condition,while the peak value in ZGDD is much higher than that in HH27.5.The flowering process of ZGDD can be reversed when switching from LD to SD condition, resulting in reversed terminal raceme,short terminal raceme,and vegetative terminal.The expression patterns of photoperiod-related genes in the flower reversion of ZGDD were identified and it was found that,GmLFY-like and GmAP1-like,the homologues of meristem identity genes LFY and AP1 showed intermediate expression patterns among SD,LD and SD-LD conditions,indicating that GmLFY-like and GmAP1-like may act as the meristem related genes in soybean.Genes involved in the up-stream photoperiodic pathway like GmGI-like and PEBP family genes expressed similarly with GmLFY-like and GmAP1-like in the early stage of flower reversion indicating they may participate in the early control of flower reversion in soybean.6.The photoperiod-related genes in soyean exhibit a rhythm of 24-h like their homologues in Arabidopsis.In SD and LD condition,GmGI has a similar expression rhythm with that in Arabidopsis in LD and is different from rice.The daily oscillation of GmCO-like genes varies from that in both AtCO and Hd1.However,the daily rhythm of GmCO-like in SD was similar with that of COL1 and COL2 in LD.The PEBP family genes showed a similar rhythm with rice in SD,and that in LD condition were different.All the results may indicate that the day length measurement in soybean is different from that both in Arabidopsis and Rice.7.A rapid and efficient platform for gene function investigation in legumes was developed, combining the simplicity and high efficiency of the Lotus corniculatus cultivar Superroot regeneration system and the availability of Agrobacterium rhizogenes-mediated transformation.Transgenic L. corniculatus plants were obtained in two and a half months and identified by molecular analysis.This system was improved by validating some parameters influencing the transformation frequency,which could reach 92%based on GUS detection.As proof of concept,transgenic Superroot plants overexpressing TaNHX2,which encodes an Na~+/H~+ antiporter,were gained and shown to have increased salt tolerance to salt stress.Transgenic Superroot plants overexpressing GmSOC1 were also obtained and they showed earlier flowering than control,indicating GmSOC1 acted as a floral inducer. It also suggested that this gene function-investigating platform could be used for antibiotic biology and developmental biology.