Strigolactones regulate Bambusa multiplex sheath senescence by promoting chlorophyll degradation

Culm sheaths are capable of photosynthesis and are an important class of non-leaf organs in bamboo plants. The source-sink interaction mechanism has been found to play an important role in the interaction between culm sheaths and internodes in Bambusa multiplex. Research on the regulatory mechanisms of culm sheath senescence is important for the study of internode growth, but reports in this regard are limited. In this study, a weighted gene co-expression network analysis was performed on transcriptome data of B. multiplex culm sheaths at different developmental stages and identified some gene modules significantly related to the typical senescence stages (SS3 and SS4). Among these modules, one module significantly associated with both SS3 and SS4 was identified, and its hub gene (BmCCD8) was a key gene of the strigolactones (SLs) synthesis pathway. To verify the relationship between SLs and culm sheath senescence, we performed experiments such as detection of endogenous hormone, treatment with exogenous hormones, transmission electron microscopic observation and detection of gene expression levels. A positive relationship was found between the SL content and the degree of sheath senescence. Treatment with the artificial SL analog GR24 resulted in a significant decrease in chlorophyll content in the sheath, while treatment with the SL synthesis inhibitor Tis108 led to a significant increase in chlorophyll content. A different response pattern to exogenous GR24 and Tis108 was also observed in genes related to the chlorophyll degradation pathway. Chloroplasts were also found to begin degradation one day after the end of exogenous GR24 treatment. Thus, we concluded that SLs may regulate culm sheath senescence by promoting chlorophyll degradation.