The Expression Pattern Of GmNMH7 Gene During Flowering Induction, Floral Development And Flowering Reversion In Soybean

Soybean is a typical short-day plant (SDP), and some photoperiod-sensitive varieties can give rise to flowering reversion after the transfer from short days to long days (SD-LD). In our laboratory, a novel experimental system consisting of 3 photoperiod treatments (SD, LD, SD13d-LD) and developmental states (flowering, continuous vegetative growth, and flowering reversion) was established by using a late soybean [Glycine max (L.) Merrill] variety Zigongdongdou (ZGDD) as material. This system can be used for studying the mechanism of photoperiod responses of SDP. In the present study, GmNMH7, a soybean homologue of NMH7 gene, was cloned with plaque hybridization from ZGDD mature flower cDNA library by using MADS-box conservative sequence as probe. The expression pattern of GmNMH7 in shoot apical meristem (SAM) of ZGDD under three different photoperiods was observed with RNA in situ hybridization. Similar work was also done in some young vegetative organs including trifoliate leaves, stems and nodules. Main results are summarized as follows:The flowering induction, floral initiation, blooming and fruiting of ZGDD plants were promoted by SD treatment. The expression of GmNMH7 could be detected in SAM before the observable floral differentiation, and during the course of flowering induction, differentiation and development of floral organs, and seeds formation in soybean.In LD treatment, ZGDD plants kept their vegetative growth and did not produce any floral organs. No transcription of GmNMH7 was detected in SAM in LD condition before the end of the experiment.Inflorescence reversion was found in over 60% of plants and short terminal racemes were produced in other plants in SD13d-LD treatment. All these plants bloomed much later than those in continuous SD. The amount of GmNMH7 transcripts in SAM was progressively reduced along with the increase of days of LD in plants that would produce reversed inflorescences. When SAM resumed to differentiate trifoliate leaves, no expression of GmNMH7 could still be detected. The expression of GmNMH7 in SAM was kept in SD13d-LD plants with short terminal racemes but the amount was less than that in continuous SD.No distinctive and regular pattern of GmNMH7 expression was found in young trifoliate leaves, young stems, and nodules at certain developmental stages, perhaps because of the limited data. The expression of GmNMH7 in these organs needs furtherinvestigation.Expression of GmNMH7 before the observable floral organogenesis provided an early evidence of flowering induction in soybean. The fact that GmNMH7 expression in SAM was controlled by photoperiods indicated that GmNMH7 gene might play some roles in flowering induction and floral development of soybean. We postulate that GmNMH7 functions like a meristem identity gene during the process of flowering and photoperiod responses in soybean.The results of this study also proved that the novel experimental system described above is effective and reliable for the study of photoperiodic responses and ontogeny of soybean.