Transcriptome analysis provides insights into the regulatory role of phytohormone in second flowering of pear

In pears, diseases and pests present a serious threat by inducing early defoliation, which in some varieties can trigger second flowering, ultimately leading to decreased yields. However, the underlying mechanisms governing second flowering remain unclear. Here, we collected branches from 'Cuiguan' pear trees that exhibited second flowering and those that did not and grew them hydroponically. We observed that buds on long branches are more prone to sprouting compared to those on short branches. Short branches with second flowering (SY) are more likely to dieback after germination than those without second flowering (SW). Long branches without second flowering (LW) show a greater tendency to sprout than those with second flowering (LY); however, LY branches face difficulties in leaf expansion after sprouting and are more susceptible to drying and dying during the early stages of sprouting. The level of indole butyric acid and zeatin was notably higher in LY and SY compared to LW and SW, whereas methyl jasmonate, abscisic acid, and gibberellin level showed a significant decrease. These findings imply that phytohormones zeatin and indole butyric acid could potentially be involved in the regulation of second flowering in pears, while methyl jasmonate seems to be responsive to disease and pest stress, thereby impacting the occurrence of second flowering. Based on RNA-seq data of leaves tissues, we identified more differentially expressed genes (DEGs) in the comparisons of SY vs. SW (10,173) than LY vs. LW (8143). Gene Ontology analysis indicated that these DEGs are involved in cell cycle regulation, hypoxia response, fatty acid metabolism, precursor metabolite production, and ribonucleoprotein complex biosynthesis. The expression patterns of nine selected genes related to flowering regulation were further validated by RT-qPCR. These findings establish a strong foundation for comprehending the regulatory mechanisms of phytohormones in the second flowering of pears and provide valuable insights for tackling this issue in agricultural practices.