Characterization and quantitative trait locus mapping of late-flowering from a Thai soybean cultivar introduced into a photoperiod-insensitive genetic background

Abstract

The timing of both flowering and maturation determine crop adaptability and productivity. Soybean (Glycine max) is cultivated across a wide range of latitudes. The molecular-genetic mechanisms for flowering in soybean have been determined for photoperiodic responses to long days (LDs), but remain only partially determined for the delay of flowering under short-day conditions, an adaptive trait of cultivars grown in lower latitudes. Here, we characterized the late-flowering (LF) habit introduced from the Thai cultivar K3 into a photoperiod-insensitive genetic background under different photo-thermal conditions, and we analyzed the genetic basis using quantitative trait locus (QTL) mapping. The LF habit resulted from a basic difference in the floral induction activity and from the suppression of flowering, which was caused by red light-enriched LD lengths and higher temperatures, during which FLOWERING LOCUS T (FT) orthologs, FT2a and FT5a, were strongly down-regulated. QTL mapping using gene-specific markers for flowering genes E2, FT2a and FT5a and 829 single nucleotide polymorphisms obtained from restriction-site associated DNA sequencing detected three QTLs controlling the LF habit. Of these, a QTL harboring FT2a exhibited large and stable effects under all the conditions tested. A resequencing analysis detected a nonsynonymous substitution in exon 4 of FT2a from K3, which converted the glycine conserved in FT-like proteins to the aspartic acid conserved in TERMINAL FLOWER 1-like proteins (floral repressors), suggesting a functional depression in the FT2a protein from K3. The effects of the remaining two QTLs, likely corresponding to E2 and FT5a, were environment dependent. Thus, the LF habit from K3 may be caused by the functional depression of FT2a and the down-regulation of two FT genes by red light-enriched LD conditions and high temperatures.

Molecular mechanisms for the photoperiodic regulation of flowering in soybean

“…Indeed, a recent study demonstrated that after J , E1 has the next most important effect on time to maturity in tropical environments (Miranda et al, 2020). Finally, GmFT2a may also have been a target for delayed flowering, as a non‐synonymous amino acid substitution in exon 4 is tightly associated with late flowering (Jiang et al, 2019; Ogiso‐Tanaka et al, 2019; Sun et al, 2019).…”

“…More recently, several other flowering time loci were shown to encode members of the well‐known FT (florigen) protein family. These FT homologs belong to the phosphatidylethanolamine binding protein (PEBP) family (Wang et al, 2015) and serve as major points of integration in flowering time control (Takeshima et al, 2016; Jiang et al, 2019; Ogiso‐Tanaka et al, 2019; Sun et al, 2019). Many FT genes are expressed in leaves under flower‐inducing conditions.…”

A Soybean Deletion Mutant That Moderates the Repression of Flowering by Cool Temperatures

“…A reduction in ambient temperature from 22 to 16 • C delays flowering in Arabidopsis (Strasser et al, 2009). This process involves a number of molecular mechanisms: (1) the occupation of histone H2A variant H2A.Z nucleosomes on the FT locus to inhibit the binding of the PIF4 transcription factor to the promoter, (2) destabilization of the CO protein by HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1, an E3 ubiquitin ligase, and (3) repression of floral integrators (FT, TWINSISTER OF FT, and SUPPRESSOR OF CONSTANS OVEREXPRESSION 1) by repressor complexes of SHORT VEGETATIVE PHASE with functional transcripts of FLOWERING LOCUS M (FLM-β) and MADS AFFECTING FLOWERING 2 (MAF2ver1) (Ratcliffe et al, 2003;Strasser et al, 2009;Jung et al, 2012;Gu et al, 2013;Lee et al, 2013;Posé et al, 2013;McClung et al, 2016;Song, 2016). The evening complex, which consists of ELF3, ELF4, and LUX ARRHYTHMO (LUX), represses its direct targets, PSEUDO RESPONSE REGULATOR 7 (PRR7), GI, and LUX, and delays flowering under cool temperatures (Mizuno et al, 2014).…”

“…The evening complex, which consists of ELF3, ELF4, and LUX ARRHYTHMO (LUX), represses its direct targets, PSEUDO RESPONSE REGULATOR 7 (PRR7), GI, and LUX, and delays flowering under cool temperatures (Mizuno et al, 2014). The loss of function of ELF3 mitigates the repression of flowering by cool temperatures to accelerate flowering under these conditions (Strasser et al, 2009). TERMINAL FLOWER 1 (TFL1) also functions in the control of flowering as a thermal sensor; ELF3 and TFL1 confer the thermal regulation of flowering through different interactions with the PHYTOCHROME B and CRYPTOCHROME photoreceptors (Strasser et al, 2009).…”

“…The loss of function of ELF3 mitigates the repression of flowering by cool temperatures to accelerate flowering under these conditions (Strasser et al, 2009). TERMINAL FLOWER 1 (TFL1) also functions in the control of flowering as a thermal sensor; ELF3 and TFL1 confer the thermal regulation of flowering through different interactions with the PHYTOCHROME B and CRYPTOCHROME photoreceptors (Strasser et al, 2009).…”