Unveiling the temporal and spatial trajectories of early resistance formation during Hylocereus undatus senescence through single-cell transcriptomics.

Fruit senescence is a complex physiological process. Previous studies have found that the formation of early resistance to fruit senescence is mainly based on phenylpropanoid biosynthesis. However, the specific response mechanisms of phenylpropanoid biosynthesis within cells are not well understood. The results showed that during the senescence process of cells related to phenylpropanoid biosynthesis, the mature sample had significantly higher phenylpropanoid biosynthesis-related cell correlations compared to the senescent sample. In the pseudotime differentiation trajectory, cells related to phenylpropanoid biosynthesis were mainly distributed in the resistance branch. A pseudotime-related gene regulatory network (GRN) was constructed. And three hub genes HuSAG12, HuNAD1, and HuDC2.15 were identified. HuSAG12 was specifically expressed in the mesocarp, while the other two genes were specifically expressed in the exocarp. They were highly expressed during the late, middle, and early stages of senescence, respectively. In the HuSAG12 RNA-silenced lines, the silencing of SAG12 negatively regulated the expression of HuDC2.15 and accelerated the fruit senescence of Hylocereus undatus. In summary, HuSAG12 likely plays a crucial role in inducing early resistance during the senescence of Hylocereus undatus by regulating flavonoid biosynthesis. This study provides new insights into the response mechanisms of phenylpropanoid biosynthesis during the dynamic senescence of fruit cells.