Genes controlling plant development have been studied in multiple plant systems. This has provided deep insights into conserved genetic pathways controlling core developmental processes including ...meristem identity, phase transitions, determinacy, stem elongation, and branching. These pathways control plant growth patterns and are fundamentally important to crop biology and agriculture. This review describes the conserved pathways that control plant development, using Arabidopsis as a model. Historical examples of how plant development has been altered through selection to improve crop performance are then presented. These examples, drawn from diverse crops, show how the genetic pathways controlling development have been modified to increase yield or tailor growth patterns to suit local growing environments or specialized crop management practices. Strategies to apply current progress in genomics and developmental biology to future crop improvement are then discussed within the broader context of emerging trends in plant breeding. The ways that knowledge of developmental processes and understanding of gene function can contribute to crop improvement, beyond what can be achieved by selection alone, are emphasized. These include using genome re-sequencing, mutagenesis, and gene editing to identify or generate novel variation in developmental genes. The expanding scope for comparative genomics, the possibility to engineer new developmental traits and new approaches to resolve gene-gene or gene-environment interactions are also discussed. Finally, opportunities to integrate fundamental research and crop breeding are highlighted.
Wheat is a major food crop, with around 765 million tonnes produced globally. The largest wheat producers include the European Union, China, India, Russia, United States, Canada, Pakistan, Australia, ...Ukraine and Argentina. Cultivation of wheat across such diverse global environments with variation in climate, biotic and abiotic stresses, requires cultivars adapted to a range of growing conditions. One intrinsic way that wheat achieves adaptation is through variation in phenology (seasonal timing of the lifecycle) and related traits (e.g., those affecting plant architecture). It is important to understand the genes that underlie this variation, and how they interact with each other, other traits and the growing environment. This review summarises the current understanding of phenology and developmental traits that adapt wheat to different environments. Examples are provided to illustrate how different combinations of alleles can facilitate breeding of wheat varieties with optimal crop performance for different growing regions or farming systems.
Transcription of the vernalization1 gene (VRN1) is induced by prolonged cold (vernalization) to trigger flowering of cereal crops, such as wheat and barley. VRN1 encodes a MADS box transcription ...factor that promotes flowering by regulating the expression of other genes. Here we use transcriptome sequencing (RNA-seq) and chromatin immunoprecipitation sequencing (ChIP-seq) to identify direct targets of VRN1. Over 500 genomic regions were identified as potential VRN1-binding targets by ChIP-seq. VRN1 binds the promoter of flowering locus T-like 1, a promoter of flowering in vernalized plants. VRN1 also targets vernalization2 and ODDSOC2, repressors of flowering that are downregulated in vernalized plants. RNA-seq identified additional VRN1 targets that might play roles in triggering flowering. Other targets of VRN1 include genes that play central roles in low-temperature-induced freezing tolerance, spike architecture and hormone metabolism. This provides evidence for direct regulatory links between the vernalization response pathway and other important traits in cereal crops.
BACKGROUND: In arabidopsis (Arabidopsis thaliana), FLOWERING LOCUS T (FT) and FLOWERING LOCUS C (FLC) play key roles in regulating seasonal flowering-responses to synchronize flowering with optimal ...conditions. FT is a promoter of flowering activated by long days and by warm conditions. FLC represses FT to delay flowering until plants experience winter. SCOPE: The identification of genes controlling flowering in cereals allows comparison of the molecular pathways controlling seasonal flowering-responses in cereals with those of arabidopsis. The role of FT has been conserved between arabidopsis and cereals; FT-like genes trigger flowering in response to short days in rice or long days in temperate cereals, such as wheat (Triticum aestivum) and barley (Hordeum vulgare). Many varieties of wheat and barley require vernalization to flower but FLC-like genes have not been identified in cereals. Instead, VERNALIZATION2 (VRN2) inhibits long-day induction of FT-like1 (FT1) prior to winter. VERNALIZATION1 (VRN1) is activated by low-temperatures during winter to repress VRN2 and to allow the long-day response to occur in spring. In rice (Oryza sativa) a VRN2-like gene Ghd7, which influences grain number, plant height and heading date, represses the FT-like gene Heading date 3a (Hd3a) in long days, suggesting a broader role for VRN2-like genes in regulating day-length responses in cereals. Other genes, including Early heading date (Ehd1), Oryza sativa MADS51 (OsMADS51) and INDETERMINATE1 (OsID1) up-regulate Hd3a in short days. These genes might account for the different day-length response of rice compared with the temperate cereals. No genes homologous to VRN2, Ehd1, Ehd2 or OsMADS51 occur in arabidopsis. CONCLUSIONS: It seems that different genes regulate FT orthologues to elicit seasonal flowering-responses in arabidopsis and the cereals. This highlights the need for more detailed study into the molecular basis of seasonal flowering-responses in cereal crops or in closely related model plants such as Brachypodium distachyon.
Grasses of the subfamily Pooideae, including important cereal crops and pasture grasses, are widespread in temperate zones. Seasonal regulation of developmental transitions coordinates the life ...cycles of Pooideae with the passing seasons so that flowering and seed production coincide with favorable conditions in spring. This review examines the molecular pathways that control the seasonal flowering responses of Pooideae and how variation in the activity of genes controlling these pathways can adapt cereals or grasses to different climates and geographical regions. The possible evolutionary origins of the seasonal flowering responses of the Pooideae are discussed and key questions for future research highlighted. These include the need to develop a better understanding of the molecular basis for seasonal flowering in perennial Pooideae and in temperate grasses outside the core Pooideae group.
Genetic analyses have identified three genes that control the vernalization requirement in wheat and barley;
VRN1,
VRN2 and
FT (
VRN3). These genes have now been isolated and shown to regulate not ...only the vernalization response but also the promotion of flowering by long days.
VRN1 is induced by vernalization and accelerates the transition to reproductive development at the shoot apex.
FT is induced by long days and further accelerates reproductive apex development.
VRN2, a floral repressor, integrates vernalization and day-length responses by repressing
FT until plants are vernalized. A comparison of flowering time pathways in cereals and
Arabidopsis shows that the vernalization response is controlled by different MADS box genes, but integration of vernalization and long-day responses occurs through similar mechanisms.
An increase in global temperatures will impact future crop yields. In the cereal crops wheat and barley, high temperatures accelerate reproductive development, reducing the number of grains per plant ...and final grain yield. Despite this relationship between temperature and cereal yield, it is not clear what genes and molecular pathways mediate the developmental response to increased temperatures. The plant circadian clock can respond to changes in temperature and is important for photoperiod-dependent flowering, and so is a potential mechanism controlling temperature responses in cereal crops. This study examines the relationship between temperature, the circadian clock, and the expression of flowering-time genes in barley (Hordeum vulgare), a crop model for temperate cereals. Transcript levels of barley core circadian clock genes were assayed over a range of temperatures. Transcript levels of core clock genes CCA1, GI, PRR59, PRR73, PRR95, and LUX are increased at higher temperatures. CCA1 and PRR73 respond rapidly to a decrease in temperature whereas GI and PRR59 respond rapidly to an increase in temperature. The response of GI and the PRR genes to changes in temperature is lost in the elf3 mutant indicating that their response to temperature may be dependent on a functional ELF3 gene.
Transcriptional activation of the VERNALIZATION1 gene mediates the acceleration of flowering by prolonged cold (vernalization) in temperate cereals. This study examined the earliest stages of the ...transcriptional response of VRN1 to low temperatures. Time-course analyses, using a sensitive quantitative PCR assay, showed that in sprouting barley seedlings VRN1 transcripts begin to accumulate within 24 hours of the onset of cold. The kinetics of the initial transcriptional response of VRN1 to cold was similar to the cold-induced genes DEHYDRIN5 (DHN5) and COLD REGULATED 14B (COR14B), but occurred at lower levels compared to cold acclimation genes or the response to longer cold treatments. Temperatures between 15 and –2 °C induced expression of VRN1 within 24 hours, with a maximal response observed between 2 and –2 °C. Transcriptional induction was also observed in undifferentiated callus cells. There were significant increases in histone acetylation levels at the VRN1 locus in response to 24-hour cold treatment. Sodium butyrate, a histone deacetylation inhibitor, triggered an increase in histone acetylation at VRN1 chromatin and elevated VRN1 transcript levels. The transcriptional response of VRN1 to short-term cold treatment was examined in near-isogenic lines that have different VRN1 genotypes, showing that an allele of the barley VRN1 gene with an insertion in the first intron and high basal expression levels has a reduced transcriptional response to short term cold treatment. This study suggests that low-temperature induction of VRN1 is a cellular response to cold triggered by the same mechanisms that mediate low-temperature induction of cold acclimation genes.
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