The interplay of growth‐regulating factor 5 and BZR1 in coregulating chlorophyll degradation in poplar

Abstract Chlorophyll (Chl) is essential for plants to carry out photosynthesis, growth and development processes. Growth‐regulating factors (GRFs) play a vital role in regulating Chl degradation in plants. However, the molecular mechanism by which GRF5 regulates Chl degradation in poplar remains unknown. Here we found that overexpression of PpnGRF5‐1 increased Chl content in leaves and promoted chloroplast development in poplar. Overexpression of PpnGRF5‐1 in poplar delayed Chl degradation induced by external factors, such as hormones, darkness and salt stress. PpnGRF5‐1 responded to brassinosteroid (BR) signalling during BR‐induced Chl degradation and reduced the expression levels of Chl degradation and senescence‐related genes. PpnGRF5‐1 inhibited the expression of Chl b reductases PagNYC1 and PagNOL . PpnGRF5‐1 could interact with PagBZR1 in the nucleus. PagBZR1 also inhibited the expression of PagNYC1 . In addition, we found that the protein–protein interaction between PagBZR1 and PpnGRF5‐1 enhanced the inhibitory effect of PpnGRF5‐1 on the Chl b reductases PagNYC1 and PagNOL . BZR1 and GRF5 ‐1 were upregulated, and NOL and NYC1 were downregulated in triploid poplars compared to diploids. This study revealed a new mechanism by which PpnGRF5‐1 regulates Chl degradation in poplars and lays the foundation for comprehensively analysing the molecular mechanism of Chl metabolism in triploid poplars.