Obstacles in sugar transportation lead to blank nut formation in hazel (Corylus heterophylla)

We examined the underlying molecular mechanisms of blank nut formation in hazelnut cultivation, which can cause yield loss. 13 C was introduced into the leaves of wild-type hazels bearing normal nuts and blank nut germplasm (BNG) with blank nuts, and 13 C abundance in leaves and fruits between these two types was compared. Photosynthetic 13 C-labeled products were rapidly transported to the bracts and nuts, and the δ 13 C value was higher in the ovule than in the bracts, shell, and parenchyma. Spatial transcriptome sequencing of normally developing and abortive ovules identified genes potentially involved in ovule abortion. In BNG, photosynthetic 13 C products synthesized in the leaves accumulated and were slowly transported outside. The δ 13 C value in the shell, parenchyma, and ovule of BNG was substantially lower than the control, accounting for 1.3–18.7 % in comparison. Based on the similarity of gene expression in each spot, six clusters, including 476 unique differentially expressed genes (DEGs) for different spatial regions, were obtained. Among these DEG clusters, only the DEGs of cluster3 were significantly enriched in biological processes related to carbohydrate metabolism and transport, and sucrose synthase ( SUS , Cor0134990.1 ) showed the highest expression abundance among these carbohydrate-metabolism-related DEGs. Based on the similarity of sequence alignment results, four SUS ( Cor0134990.1 ) mutants were identified in Arabidopsis, and their seed size was significantly smaller than that of the wild-type. In addition to SUS , some important genes that may regulate hazelnut ovule development were identified, providing new insights into the blank hazelnut formation mechanisms. • The δ 13 C value in the ovule was higher than that in the bracts, shell, and parenchyma. • In blank nut germplasm, the 13 C photosynthetic products were transported outside slowly. • Spatial transcriptome sequencing was used to determine the vital regulation genes in ovule. • The four sus mutants generated smaller seeds.