Transcriptome Analysis of Developing Wheat Grains at Rapid Expanding Phase Reveals Dynamic Gene Expression Patterns

SIMPLE SUMMARY: Understanding the regulatory mechanism underlying grain development is essential for wheat improvement. The early grain expanding phase boasts critical biological events like embryogenesis and initiation of grain filling. RNA sequencing analysis of this developmental stage revealed dynamic expressions of genes related to cell division, starch biosynthesis, and hormone biosynthesis. An unbalanced expression among triads may play critical roles as shown by multiple enriched metabolic pathways. Our work demonstrated complex regulation mechanisms in early grain development and provided useful information for future wheat improvement. ABSTRACT: Grain development, as a vital process in the crop’s life cycle, is crucial for determining crop quality and yield. The wheat grain expanding phase is the early process involving the rapid morphological changes and initiation of grain filling. However, little is known about the molecular basis of grain development at this stage. Here, we provide a time-series transcriptome profile of developing wheat grain at 0, 2, 4, 6, 8, and 10 days after pollination of the wheat landrace Chinese Spring. A total of 26,892 differentially expressed genes, including 1468 transcription factors, were found between adjacent time points. Co-expression cluster analysis and Gene Ontology enrichment revealed dynamic expressions of cell division and starch biosynthesis related structural genes and transcription factors. Moreover, diverse, differential and drastically varied expression trends of the key genes related to hormone metabolism were identified. Furthermore, ~30% of triads showed unbalanced expression patterns enriching for genes in multiple pivotal metabolic pathways. Hormone metabolism related genes, such as YUC10 (YUCCA flavin-containing monooxygenase 10), AOS2 (allene oxide synthase 2), CYP90D2 (cytochrome P450 90D2), and CKX1 (cytokinin dehydrogenase 1), were dominantly contributed by A or D homoeologs of the triads. Our study provided a systematic picture of transcriptional regulation of wheat grains at the early grain expanding phase which should deepen our understanding of wheat grain development and help in wheat yield improvement.