Soybean is highly sensitive to photoperiod, which affects flowering time and plant architecture. The flowering time of soybean, as well as its overall plant architecture, particularly plant height, will change as a function of photoperiod, thus potentially greatly influencing yield.

Due to their photoperiod sensitivity, each soybean cultivar is adapted to a narrow range of latitudes for maximal yield, thus limiting a wider distribution of elite soybean cultivars and affecting the stable and high yield of soybean in China.

A research team led by Prof. XIA Zhengjun’s from Northeast Institute of Geography and Agroecology of the Chinese Academy of Sciences has made important progress on molecular mechanism on how E1 regulates photoperiodic flowering.

Their study was published in Plant Physiology.

The encoded E1 protein is proven to be a transcriptional repressor. Based on RNA-Sequencing (RNA-Seq) analysis, the expression of seven GmMDE genes (Glycine max MADS-box genes) downregulated by E1 MADS-box genes (GmMDEs) was suppressed when E1 was overexpressed and promoted when E1 was knocked out through CRISPR/Cas9-mediated mutagenesis.

These GmMDEs exhibited similar tissue specificity and expression patterns. Taking two GmMDEs, GmMDE05 and GmMDE06 as example, E1 epigenetically silences their expression by directly binding to their promoters to increase H3K27me3 levels.

GmMDE06 was focused to explore the function of GmMDEs in flowering time. Overexpression of GmMDE06 promoted flowering and post-flowering termination of stem growth.

The late flowering phenotype of E1-overexpressing soybean lines was reversed by overexpression of GmMDE06. placing GmMDE06 downstream of E1. GmMDE06 also promoted post-flowering termination of stem growth by repressing the expression of the shoot identity gene Dt1.

Overexpression of GmMDE06 increased the expression of the soybean FLOWERING LOCUS T orthologs GmFT2a and GmFT5a, leading to a feedback upregulation of GmMDE, indicating that GmMDE and GmFT2a/GmFT5a form a positive regulatory feedback loop promoting flowering.

The E1-GmMDEs-GmFT2a/5a-Dt1 signaling pathway illustrates how soybean responds to photoperiod by modulating flowering time and post-flowering stem termination.

This study uncovered the signaling pathway downstream of E1. which the link photoperiodic pathway and growth habit regulation pathway. The study facilitate soybean molecular design breeding for high yield and wide adaptation.

Proposed model for E1 regulation of the photoperiodic response of soybean(Image by ZHAI Hong et al.)

Contact:

ZHAI HongNortheast Institute of Geography and Agroecology

E-mail: zhaih@iga.ac.cn