GmFULc Is Induced by Short Days in Soybean and May Accelerate Flowering in Transgenic Arabidopsis thaliana

LsFUL-LsSMU2 module positively controls bolting time in leaf lettuce (Lactuca sativa L.) under high temperature

High temperature (HT) is an environmental factor that considerably affects plant physiology, development, crop yield, and economic value. HT can cause diseases and early bolting of leaf lettuce, thereby reducing the yield and quality of leaf lettuce. Herein, we used two leaf lettuce (Lactuca sativa L.) cultivars (bolting-resistant 'S24' and bolting-sensitive 'S39') to investigate the key factors and molecular mechanism impacting bolting. We found that 14 MADS-box genes implicated in bolting and flowering, LsMADS54 (also referred to as L. sativa FRUITFULL, LsFUL), was significantly up-regulated 1000 times after 5-d HT treatment and that HT-induced up-regulation of LsFUL was higher in bolting-sensitive than in resistant cultivars. The overexpression lines of LsFUL exhibited an earlier bolting time than that in the non-transformed 'S39'(CK). However, the RNA interference, and CRISPR-Cas9-mediated knockout lines of LsFUL exhibited a later bolting time than that in CK. In addition, we found that L. sativa SUPPRESSORS OF MEC-8 AND UNC-52 PROTEIN 2 (LsSMU2) and L. sativa CONSTANS-LIKE PROTEIN 5 (LsCOL5) interact with LsFUL, and these interactions could stimulate or prevent bolting. We observed that elevated temperature stimulated the abundance of LsSMU2 in the stem, which collaborated with LsFUL to accelerate bolting. Conversely, room temperature (RT) condition led to relatively more stable LsCOL5, which worked with LsFUL to postpone bolting. In summary, our findings demonstrate a molecular regulatory module of LsSMU2-LsFUL associated with HT-induced premature bolting, which serves as a reference for understanding HT-induced premature bolting phenomenon in leaf lettuce.

The MADS-box transcription factor GmFULc promotes GmZTL4 gene transcription to modulate maturity in soybean

Flowering time and maturity are crucial agronomic traits that affect the regional adaptability of soybean plants. The development of soybean cultivars with early maturity adapted to longer days and colder climates of high latitudes is very important for ensuring normal ripening before frost begins. FUL belongs to the MADS-box transcription factor family and has several duplicated members in soybeans. In this study, we observed that overexpression of GmFULc in the Dongnong 50 cultivar promoted soybean maturity, while GmFULc knockout mutants exhibited late maturity. Chromatin immunoprecipitation sequencing (ChIP-seq) and RNA sequencing (RNA-seq) revealed that GmFULc could bind to the CArG, bHLH and homeobox motifs. Further investigation revealed that GmFULc could directly bind to the CArG motif in the promoters of the GmZTL3 and GmZTL4 genes. Overexpression of GmZTL4 promoted soybean maturity, whereas the ztl4 mutants exhibited delayed maturity. Moreover, we found that the cis element box 4 motif of the GmZTL4 promoter, a motif of light response elements, played an important role in controlling the growth period. Deletion of this motif shortened the growth period by increasing the expression levels of GmZTL4. Functional investigations revealed that short-day treatment promoted the binding of GmFULc to the promoter of GmZTL4 and inhibited the expression of E1 and E1Lb, ultimately resulting in the promotion of flowering and early maturation. Taken together, these findings suggest a novel photoperiod regulatory pathway in which GmFULc directly activates GmZTL4 to promote earlier maturity in soybean.

Molecular breeding for improvement of photothermal adaptability in soybean

Soybean (Glycine max (L.) Merr.) is a typical short-day and temperate crop that is sensitive to photoperiod and temperature. Responses of soybean to photothermal conditions determine plant growth and development, which affect its architecture, yield formation, and capacity for geographic adaptation. Flowering time, maturity, and other traits associated with photothermal adaptability are controlled by multiple major-effect and minor-effect genes and genotype-by-environment interactions. Genetic studies have identified at least 11 loci (E1-E4, E6-E11, and J) that participate in photoperiodic regulation of flowering time and maturity in soybean. Molecular cloning and characterization of major-effect flowering genes have clarified the photoperiod-dependent flowering pathway, in which the photoreceptor gene phytochrome A, circadian evening complex (EC) components, central flowering repressor E1, and FLOWERING LOCUS T family genes play key roles in regulation of flowering time, maturity, and adaptability to photothermal conditions. Here, we provide an overview of recent progress in genetic and molecular analysis of traits associated with photothermal adaptability, summarizing advances in molecular breeding practices and tools for improving these traits. Furthermore, we discuss methods for breeding soybean varieties with better adaptability to specific ecological regions, with emphasis on a novel strategy, the Potalaization model, which allows breeding of widely adapted soybean varieties through the use of multiple molecular tools in existing elite widely adapted varieties.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01406-z.

MADS-Box Subfamily Gene GmAP3 from Glycine max Regulates Early Flowering and Flower Development

AP3 has been studied and is reported to affect structural changes in floral organs in various plants. However, the function of the soybean AP3 genes in flower development is unknown. Here, the full-length cDNA sequence of GmAP3 was obtained by RACE and it was verified that it belongs to the MADS-box subfamily by a bioinformatics analysis. The expression of GmAP3 is closely related to the expression of essential enzyme genes related to flower development. Yeast two-hybrid assays demonstrated that GmAP3 interacts with AP1 to determine the identity of flower organ development. A follow-up analysis showed that overexpression of the GmAP3 gene advanced flowering time and resulted in changes in floral organ morphology. The average flowering time of overexpressed soybean and tobacco plants was 6-8 days earlier than that of wild-type plants, and the average flowering time of gene-edited soybean and tobacco plants was 6-11 days later than that of wild-type plants. In conclusion, GmAP3 may directly or indirectly affect the flower development of soybean. The results of this study lay the foundation for further research on the biological functions of MADS transcriptional factors in soybeans.

Five NUCLEAR FACTOR-Y subunit B genes in rapeseed (Brassica napus) promote flowering and root elongation in Arabidopsis

Heterologous expression of BnNF-YB2, BnNF-YB3, BnNF-YB4, BnNF-YB5, or BnNF-YB6 from rapeseed promotes the floral process and also affects root development in Arabidopsis. The transcriptional regulator NUCLEAR FACTOR-Y (NF-Y) is a heterotrimeric complex composed of NF-YA, NF-YB, and NF-YC proteins and is ubiquitous in yeast, animal, and plant systems. In this study, we found that five NF-YB proteins from rapeseed (Brassica napus), including BnNF-YB2, BnNF-YB3, BnNF-YB4, BnNF-YB5, and BnNF-YB6 (BnNF-YB2/3/4/5/6), all function in photoperiodic flowering and root elongation. Sequence alignment and phylogenetic analysis showed that BnNF-YB2/3 and BnNF-YB4/5/6 were clustered with Arabidopsis AtNF-YB2 and AtNF-YB3, respectively, implying that these NF-YBs are evolutionarily and functionally conserved. In support of this hypothesis, the heterologous expression of individual BnNF-YB2, 3, 4, 5, or 6 in Arabidopsis promoted early flowering under a long-day photoperiod. Further analysis suggested that BnNF-YB 2/3/4/5/6 elevated the expression of key downstream flowering time genes including CO, FT, LFY and SOC1. Promoter-GUS fusion analysis showed that the five BnNF-YBs were expressed in a variety of tissues at various developmental stages and GFP fusion analysis revealed that all BnNF-YBs were localized to the nucleus. In addition, we demonstrated that the heterologous expression of individual BnNF-YB2/3/4/5/6 in Arabidopsis promoted root elongation and increased the number of root tips formed under both normal and treatment with simulators of abiotic stress conditions.

CONSTANS Polymorphism Modulates Flowering Time and Maturity in Soybean

CONSTANS (CO) plays a critical role in the photoperiodic flowering pathway. However, the function of soybean CO orthologs and the molecular mechanisms in regulating flowering remain largely unknown. This study characterized the natural variations in CO family genes and their association with flowering time and maturity in soybeans. A total of 21 soybean CO family genes (GmCOLs) were cloned and sequenced in 128 varieties covering 14 known maturity groups (MG 0000-MG X from earliest to latest maturity). Regarding the whole genomic region involving these genes, GmCOL1, GmCOL3, GmCOL8, GmCOL9, GmCOL10, and GmCOL13 were conserved, and the remaining 15 genes showed genetic variation that was brought about by mutation, namely, all single-nucleotide polymorphisms (SNPs) and insertions-deletions (InDels). In addition, a few genes showed some strong linkage disequilibrium. Point mutations were found in 15 GmCOL genes, which can lead to changes in the potential protein structure. Early flowering and maturation were related to eight genes (GmCOL1/3/4/8/13/15/16/19). For flowering and maturation, 11 genes (GmCOL2/5/6/14/20/22/23/24/25/26/28) expressed divergent physiognomy. Haplotype analysis indicated that the haplotypes of GmCOL5-Hap2, GmCOL13-Hap2/3, and GmCOL28-Hap2 were associated with flowering dates and soybean maturity. This study helps address the role of GmCOL family genes in adapting to diverse environments, particularly when it is necessary to regulate soybean flowering dates and maturity.

Functional Redundancy of FLOWERING LOCUS T 3b in Soybean Flowering Time Regulation

Photoperiodic flowering is an important agronomic trait that determines adaptability and yield in soybean and is strongly influenced by FLOWERING LOCUS T (FT) genes. Due to the presence of multiple FT homologs in the genome, their functions in soybean are not fully understood. Here, we show that GmFT3b exhibits functional redundancy in regulating soybean photoperiodic flowering. Bioinformatic analysis revealed that GmFT3b is a typical floral inducer FT homolog and that the protein is localized to the nucleus. Moreover, GmFT3b expression was induced by photoperiod and circadian rhythm and was more responsive to long-day (LD) conditions. We generated a homozygous ft3b knockout and three GmFT3b-overexpressing soybean lines for evaluation under different photoperiods. There were no significant differences in flowering time between the wild-type, the GmFT3b overexpressors, and the ft3b knockouts under natural long-day, short-day, or LD conditions. Although the downstream flowering-related genes GmFUL1 (a, b), GmAP1d, and GmLFY1 were slightly down-regulated in ft3b plants, the floral inducers GmFT5a and GmFT5b were highly expressed, indicating potential compensation for the loss of GmFT3b. We suggest that GmFT3b acts redundantly in flowering time regulation and may be compensated by other FT homologs in soybean.