Search

Soybean is an important model crop for photoperiodic response studies in plants and contributes significantly to the study of plant development and physiology in the past century. Because soybean plant is much bigger in size and longer in life cycle than Arabidopsis, it needs much more space for growth and time for investigation, which significantly hamper the efficiency of research. In the current study, we tested the photoperiodic response of a distinctive artificially-made cotyledon-only plant (COP) using a photoperiod-sensitive soybean variety Zigongdongdou (ZGDD) and other varieties with diverse sensitivity to photoperiod. ZGDD COPs flowered 39.4 ± 2.5 d after emergence under short-day conditions but maintained vegetative growth under long-day and night break conditions, which is similar to the case in the intact ZGDD plants. The COPs of early-maturing and medium-maturing soybean varieties also grew and flowered normally under natural day-length conditions. At the molecular level, the key genes in the photoperiodic pathway such as E1, GmFT1a, GmFT2a, and GmFT5a in the COPs also showed the same photoperiod sensitivity as in the intact plants. In addition, a simpler material of COP with only one cotyledon and root was generated and found to be sensitive to photoperiod as well. Notably, the COPs are only one-fifth the height of intact plants and one-third the maximum diameter of the intact plants grown in chambers 30 d after emergence. Based on COPs, we established a novel experimental system characterized by an entire photoperiodic response and longer longevity of cotyledons in addition to small plant size, ensuring the consistency, reliability, and stability of plant materials. COPs have the potential to be a novel model material for studies of the developmental biology of soybean and other dicots.

Additional file 1: Table S1. Basic statistics for the polymorphic sites in the soybean chloroplast and mitochondrial genomes.

Additional file 2: Table S2. Polymorphic sites with a high or moderate impact in chloroplast genomes.

Additional file 3: Table S3. Polymorphic sites with a high or moderate impact in mitochondrial genomes.

Soybean (Glycine max), a typical short‐day plant (SDP) domesticated in temperate regions, has expanded to high latitudes where daylengths are long from soybean emergence to bloom, but rapidly decrease from seed filling to maturity. Cotyledons are well known as the major storage organs in seeds, but it is unclear whether developing cotyledons store flowering substances at filling stage in SD for upcoming seedlings, or instead respond to photoperiod for floral induction after emergence of matured seeds in long‐day (LD). Here, we report that cotyledons accelerate flowering of early‐maturing varieties not resulting from stored floral stimuli but by perceiving photoperiod after emergence. We found that light signal is indispensable to activate cotyledons for floral induction, and flowering promoting gene GmFT2a is required for cotyledon‐dependent floral induction via upregulation of floral identity gene GmAP1. Interestingly, cotyledons are competent to support the entire life cycle of a cotyledon‐only plant to produce seeds, underlying a new photoperiod study system in soybean and other dicots. Taken together, these results demonstrate a substantial role for cotyledons in flowering process, whereby we propose a ‘cotyledon‐based self‐reliance’ model highlighting floral induction from emergence as a key ecological adaptation for rapid flowering of SDPs grown in LD environments at high latitudes., The cotyledons induce soybean flowering by expressing flowering promoting gene GmFT2a after perceiving light signals at seedling stage. The cotyledon‐dependent floral induction accelerates the flowering of early‐maturing varieties in long‐day and facilitate them adapting to high latitudes.

Additional file 1.

Day length has an important influence on flowering and growth habit in many plant species. In crops such as soybean, photoperiod sensitivity determines the geographical range over which a given cultivar can grow and flower. The soybean genome contains ~10 genes homologous to FT, a central regulator of flowering from Arabidopsis thaliana. However, the precise roles of these soybean FTs are not clearly. Here we show that one such gene, GmFT2b, promotes flowering under long‐days (LDs). Overexpression of GmFT2b upregulates expression of flowering‐related genes which are important in regulating flowering time. We propose a ‘weight’ model for soybean flowering under short‐day (SD) and LD conditions. Furthermore, we examine GmFT2b sequences in 195 soybean cultivars, as well as flowering phenotypes, geographical distributions and maturity groups. We found that Hap3, a major GmFT2b haplotype, is associated with significantly earlier flowering at higher latitudes. We anticipate our assay to provide important resources for the genetic improvement of soybean, including new germplasm for soybean breeding, and also increase our understanding of functional diversity in the soybean FT gene family., In an effort to understand the molecular genetic basis of flowering time in soybean, we have isolated and characterized GmFT2b, a soybean FT gene homolog. We used overexpression and CRISPR/Cas9‐induced targeted gene mutations to show that GmFT2b regulates flowering in soybean, but only under long days. We also sequenced this gene from 195 soybean cultivars in different maturity groups (MGs). Our analysis showed that one GmFT2b haplotype, Hap3, is found only in early‐maturing cultivars in MGs 0–2, and correlates with their ability to flower in environments located at high latitudes in northeastern China.