Time-course transcriptome analysis of the two types of seeds provides insights into seed shape differentiation in wax gourd

Wax gourd is an important vegetable crop in Cucurbitaceae. There are two shapes of wax gourd seeds, bilateral and unilateral. Bilateral seeds are more popular than unilateral seeds because they germinate faster along with a higher germination rate. Previously, we identified the seed shape determination gene YABBY4 through genetic mapping and genome-wide association study. However, the molecular mechanisms underlying seed shape differentiation remain elusive. In this study, the B214 variety containing bilateral seeds and the B227 variety containing unilateral seeds were subjected to time-course transcriptome analysis. Our results showed that genes related to secondary metabolite biosynthesis were differentially expressed between B214 and B227 seeds at all stages, and some lignin biosynthesis-related genes were highly expressed in B214 seeds at the later stages. At the early stages, genes associated with cell periphery, plasma membrane, plant hormone signal transduction, and MAPK signaling pathway were more active. Catalytic activity, biosynthetic, and metabolic process-related genes were differentially expressed at the later stages. Together, our findings dissect the transcriptomic differences between the two types of seeds and gain insights into the regulatory networks of seed shape differentiation in wax gourd.