OsFTIP1-Mediated Regulation of Florigen Transport in Rice Is Negatively Regulated by the Ubiquitin-Like Domain Kinase OsUbDKγ4

FE Controls the Transcription of Downstream Flowering Regulators Through Two Distinct Mechanisms in Leaf Phloem Companion Cells

In the facultative long-day plant Arabidopsis thaliana, FLOWERING LOCUS T (FT), encoding the mobile hormone florigen, plays an essential role in modulating the optimal timing of flowering to ensure reproductive success. Under inductive long-day conditions, the transcription of FT is activated by the CONSTANS (CO)/NUCLEAR FACTOR-Y (NF-Y) protein complex in leaf phloem companion cells. FT is transported to the shoot apical meristem through interaction with florigen transporters, such as SODIUM POTASSIUM ROOT DEFECTIVE 1 (NaKR1). Some regulators involved in photoperiod-dependent FT function have been reported previously; however, the molecular mechanism that coordinates FT protein synthesis and transport efficiently needs to be investigated. The present study examined the role of an Myb-related transcription factor, FE, in the activation of FT gene transcription and FT protein transport. Expression analysis using FE-inducible systems and chromatin immunoprecipitation assays showed that FE directly bound to the FT and NaKR1 promoters and activated the transcription of downstream target genes. FE failed to activate FT expression without CO function, whereas FE-mediated NaKR1 induction was not affected by CO function. Taken together, our data indicate that FE regulates the transcription of FT and florigen transporter genes via different mechanisms.

Molecular function of florigen

Florigen is a mobile flowering signal in plants that has a strong impact on plant reproduction and is considered one of the important targets for crop improvement. At the molecular level, florigen is represented as a protein product encoded by the FLOWERING LOCUS T (FT) gene, which is highly conserved across flowering plants and thus the understanding of this protein is expected to be applied to the improvement of many crops. Recent advances in molecular genetics, cell biology and structural biology in plants revealed the presence of intercellular receptors for florigen, a transcriptional complex essential for florigen to function, and also shed light on the molecular basis of pleiotropic function of florigen beyond flowering. Furthermore, cutting-edge technologies, such as live cell imaging and next generation sequencing revealed the precise distribution of florigen and transcriptional targets of the florigen activation complex (FAC) during early stages of floral transition. These understandings will help future crop improvement through the regulation of flowering and other plant developmental processes.

Assessing and Exploiting Functional Diversity in Germplasm Pools to Enhance Abiotic Stress Adaptation and Yield in Cereals and Food Legumes

There is a need to accelerate crop improvement by introducing alleles conferring host plant resistance, abiotic stress adaptation, and high yield potential. Elite cultivars, landraces and wild relatives harbor useful genetic variation that needs to be more easily utilized in plant breeding. We review genome-wide approaches for assessing and identifying alleles associated with desirable agronomic traits in diverse germplasm pools of cereals and legumes. Major quantitative trait loci and single nucleotide polymorphisms (SNPs) associated with desirable agronomic traits have been deployed to enhance crop productivity and resilience. These include alleles associated with variation conferring enhanced photoperiod and flowering traits. Genetic variants in the florigen pathway can provide both environmental flexibility and improved yields. SNPs associated with length of growing season and tolerance to abiotic stresses (precipitation, high temperature) are valuable resources for accelerating breeding for drought-prone environments. Both genomic selection and genome editing can also harness allelic diversity and increase productivity by improving multiple traits, including phenology, plant architecture, yield potential and adaptation to abiotic stresses. Discovering rare alleles and useful haplotypes also provides opportunities to enhance abiotic stress adaptation, while epigenetic variation has potential to enhance abiotic stress adaptation and productivity in crops. By reviewing current knowledge on specific traits and their genetic basis, we highlight recent developments in the understanding of crop functional diversity and identify potential candidate genes for future use. The storage and integration of genetic, genomic and phenotypic information will play an important role in ensuring broad and rapid application of novel genetic discoveries by the plant breeding community. Exploiting alleles for yield-related traits would allow improvement of selection efficiency and overall genetic gain of multigenic traits. An integrated approach involving multiple stakeholders specializing in management and utilization of genetic resources, crop breeding, molecular biology and genomics, agronomy, stress tolerance, and reproductive/seed biology will help to address the global challenge of ensuring food security in the face of growing resource demands and climate change induced stresses.