Regulatory responses to phosphorus deficiency in pecan (Carya illinoinensis): transcriptomic and microscopic approaches.

Phosphorus (P) deficiency in the soil significantly limits pecan growth due to its low availability and mobility. However, the molecular mechanisms underlying these responses to P deficiency are unclear. Therefore, this study aimed to describe adaptive strategies in pecan under varying P levels using microscopic and transcriptomic approaches to investigate pecans' adaptive mechanisms under three different P levels: normal phosphorus control (CK), low phosphorus (LP), and no-phosphorus (NP) deficiency. Compared with CK, we obtained 804 and 2,044 differentially expressed genes (DEGs) for LP and NP deficiency. The hierarchical clustering analysis categorized these DEGs into seven modules with distinct expression profiles. Functional enrichment analyses revealed that glycolysis and starch metabolism-related DEGs were consistently down-regulated, indicating a common response to LP and NP. Conversely, polysaccharide synthesis DEGs were considerably up-regulated under NP stress. The expression patterns of related DEGs were further validated using reverse transcription quantitative PCR (RT-qPCR). Our microscopic observations were consistent with these findings, showing increased root tip starch granules under P deficiency stress. Together, these findings suggest that pecan seedlings showed two coordinated responses to P deficiency: reduced expression of catabolic pathways and increased polysaccharide biosynthesis under NP, accompanied by higher root-tip starch granules and enhanced root architecture. This study elucidates the response of pecan to P deficiency and highlights potential targets for improving phosphorus use efficiency in woody oil crops.