A Spatial Transcriptome for Germinating Barley Grain

A spatial resolved transcriptome for germinating barley grain was obtained for over 14,000 genes at 0, 1, 3 6 and 24 hours after imbibition. The spatial expression of a number of genes was validated using in-situ PCR, quantitative comparison to bulk RNA-seq reveal good correlations, despite the differences in the methodologies, and marker gene definition for tissues/clusters was consistent with previous gene specific studies. Targeted analysis of genes encoding aquaporins, crucial for water and ion movement during germination, revealed specific spatial expression patterns for gene members, and the tissue specific changes in gene members over time. Highly restricted spatial (and temporal) expression patterns were observed for genes encoding cell wall and transcription factors, e.g. one of the strongest expressed transcription factors was a bZIP family member that responds to germinating promoting Karrikin. It's expression was restricted to the scutellum and the adjacent endosperm (0-3 HAI) and declined afterwards. Discovery-based bio-informatic approaches revealed thousands of genes displayed a spatially restricted pattern within tissues, with gene ontology revealing enriched categories such as auxin related functions of transport and response factors displaying distinct spatial expression patterns in tissues. This provides unprecedented spatial resolved cellular map for germination and specific genes to target for functional genomics to define cellular restricted processes in tissues during germination. Overall design: Germinating barley grain were snap-frozened and longitudinal sectioned. The section of barley grains were sequenced and analysized using Visium protocol (10X Genomics). .