GIGANTEA accelerates wheat heading time through gene interactions converging on FLOWERING LOCUS T1

Subgenome-informed statistical modeling of transcriptomes in 25 common wheat accessions reveals cis- and trans-regulation architectures

Common wheat is an allohexaploid, where it is difficult to obtain homoeolog-distinguished transcriptome data. Lasy-Seq, a type of 3' RNA-seq, is technology efficient at obtaining homoeolog-distinguished transcriptomes. Here, we applied Lasy-Seq to obtain transcriptome data from the seedlings, second leaves, and root tips of 25 common wheat lines mainly from East Asia. Roots and seedlings were similar to each other in transcriptome profiles, but they were different from the leaves. We then asked how three homoeologous genes from different subgenomes (i.e. triads) show different levels of expression. Specifically, we examined the effects of subgenomes, lines, and their interaction on the expression levels of each homoeolog triad, separately in each tissue. Of the 19 805 homoeolog triads, 51-55% showed significant effect of subgenome, suggesting cis-regulation, whereas 24-30% showed significant effect line, suggesting trans-regulation. We also found that 7.7-9.0% triads showed significant effects of the interaction. Hierarchical clustering and co-trans regulation network analysis of homoeolog triads revealed that the patterns of expression polymorphisms among the lines were shared in different genes. Our results also implied that expression variation between lines is caused by changes in a smaller number of common trans-factors. We performed gene ontology (GO)-term enrichment analysis using newly annotated and substantially improved GO annotations, which revealed that GO terms related to each tissue-type function were enriched in genes expressed in the leaves and roots. Our information provides fundamental knowledge for the future breeding of plants possessing complex gene regulatory networks such as common wheat.

Dissecting the genetic architecture of key agronomic traits in lettuce using a MAGIC population

BACKGROUND

Lettuce is a globally important leafy vegetable that exhibits diverse horticultural types and strong population structure, which complicates genetic analyses. To address this challenge, we develop the first multi-parent, advanced generation inter-cross (MAGIC) population for lettuce using 16 diverse founder lines.

RESULTS

Whole-genome sequencing of the 16 founder lines and 381 inbred progeny reveal minimal population structure, enabling informative genome-wide association studies (GWAS). GWAS of the lettuce MAGIC population identifies numerous loci associated with key agricultural traits, including 51 for flowering time, 11 for leaf color, and 5 for leaf shape. Notably, loss-of-function mutations in the LsphyB and LsphyC genes, encoding phytochromes B and C, dramatically delay flowering in lettuce, which is in striking contrast to many other plant species. This unexpected finding highlights the unique genetic architecture controlling flowering time in lettuce. The wild-type LsTCP4 gene plays critical roles in leaf flatness and its expression level is negatively correlated with leaf curvature. Additionally, a novel zinc finger protein (ZFP) gene is required for the development of lobed leaves; a point mutation leads to its loss of function and consequently converted lobed leaves to non-lobed leaves, as exhibited by most lettuce cultivars.

CONCLUSIONS

The MAGIC population's lack of structure and high mapping resolution enables the efficient dissection of complex traits. The identified loci and candidate genes provide significant genetic resources for improving agronomic performance and leaf quality in lettuce.

Molecular genetic regulation of the vegetative-generative transition in wheat from an environmental perspective

The key to the wide geographical distribution of wheat is its high adaptability. One of the most commonly used methods for studying adaptation is investigation of the transition between the vegetative-generative phase and the subsequent intensive stem elongation process. These processes are determined largely by changes in ambient temperature, the diurnal and annual periodicity of daylength, and the composition of the light spectrum. Many genes are involved in the perception of external environmental signals, forming a complex network of interconnections that are then integrated by a few integrator genes. This hierarchical cascade system ensures the precise occurrence of the developmental stages that enable maximum productivity. This review presents the interrelationship of molecular-genetic pathways (Earliness per se, circadian/photoperiod length, vernalization - cold requirement, phytohormonal - gibberellic acid, light perception, ambient temperature perception and ageing - miRNA) responsible for environmental adaptation in wheat. Detailed molecular genetic mapping of wheat adaptability will allow breeders to incorporate new alleles that will create varieties best adapted to local environmental conditions.

An eight-founder wheat MAGIC population allows fine-mapping of flowering time loci and provides novel insights into the genetic control of flowering time

Flowering time synchronizes reproductive development with favorable environmental conditions to optimize yield. Improved understanding of the genetic control of flowering will help optimize varietal adaptation to future agricultural systems under climate change. Here, we investigate the genetic basis of flowering time in winter wheat (Triticum aestivum L.) using an eight-founder multi-parent advanced generation intercross (MAGIC) population. Flowering time data was collected from field trials across six growing seasons in the United Kingdom, followed by genetic analysis using a combination of linear modelling, simple interval mapping and composite interval mapping, using either single markers or founder haplotype probabilities. We detected 57 quantitative trait loci (QTL) across three growth stages linked to flowering time, of which 17 QTL were identified only when the major photoperiod response locus Ppd-D1 was included as a covariate. Of the 57 loci, ten were identified using all genetic mapping approaches and classified as 'major' QTL, including homoeologous loci on chromosomes 1B and 1D, and 4A and 4B. Additional Earliness per se flowering time QTL were identified, along with growth stage- and year-specific effects. Furthermore, six of the main-effect QTL were found to interact epistatically with Ppd-D1. Finally, we exploited residual heterozygosity in the MAGIC recombinant inbred lines to Mendelize the Earliness per se QTL QFt.niab-5A.03, which was confirmed to modulate flowering time by at least four days. This work provides detailed understanding of the genetic control of phenological variation within varieties relevant to the north-western European wheat genepool, aiding informed manipulation of flowering time in wheat breeding.

Phenotypic and transcriptome profiling of spikes reveals the regulation of light regimens on spike growth and fertile floret number in wheat

The spike growth phase is critical for the establishment of fertile floret (grain) numbers in wheat (Triticum aestivum L.). Then, how to shorten the spike growth phase and increase grain number synergistically? Here, we showed high-resolution analyses of floret primordia (FP) number, morphology and spike transcriptomes during the spike growth phase under three light regimens. The development of all FP in a spike could be divided into four distinct stages: differentiation (Stage I), differentiation and morphology development concurrently (Stage II), morphology development (Stage III), and polarization (Stage IV). Compared to the short photoperiod, the long photoperiod shortened spike growth and stimulated early flowering by shortening Stage III; however, this reduced assimilate accumulation, resulting in fertile floret loss. Interestingly, long photoperiod supplemented with red light shortened the time required to complete Stages I-II, then raised assimilates supply in the spike and promoted anther development before polarization initiation, thereby increasing fertile FP number during Stage III, and finally maintained fertile FP development during Stage IV until they became fertile florets via a predicted dynamic gene network. Our findings proposed a light regimen, critical stages and candidate regulators that achieved a shorter spike growth phase and a higher fertile floret number in wheat.