Comprehensive genome-wide characterization of calmodulin-binding protein 60 gene family reveals PtCBP60E1 enhances the pathogen resistance in poplar

The calmodulin-binding protein 60 (CBP60) family members play pivotal roles in plant immunity in plants. Most studies have concentrated on AtCBP60a , AtCBP60b and AtCBP60g in Arabidopsis thaliana . However, there are few reports on the CBP60 gene family in woody plants, particularly the function of CBP60e in plant-pathogen interactions. In this investigation, 14 Populus trichocarpa ( Pt ) CBP60 ( PtCBP60 ) genes were identified and these genes were unevenly dispersed across eight chromosomes. The detection of collinearity and the presence of tandem gene clusters suggested that segmental duplication and tandem duplication might be the critical impetus for expanding gene members in poplar. Notably, PtCBP60E1 and PtCBP60E2 not only showed segmental duplication events, but shared similar physicochemical properties. PtCBP60E1 was further evaluated by the temporal expression pattern analysis at different hours post-inoculation (hpi) with Colletotrichum gloeosporioides , which showed that its expression was significantly induced (9.7-fold) at 24 hpi. Intriguingly, the area of leaf lesions (2.8 mm 2 ) in overexpression (OE) of PtCBP60E1 (OE-31) lines was notably smaller than that (15.35 mm 2 ) in non-transgenic poplar 84 K (wild-type, WT) lines at 3 days post-inoculation. Higher ROS accumulation was detected in OE lines after C. gloeosporioides infection compared to WT lines. These results showed that PtCBP60E1 positively regulated the resistance response of poplar to C. gloeosporioides infection. Overall, this study provided a comprehensive characterization of the PtCBP60 gene family in poplar and identified PtCBP60E1 as an essential regulatory gene in response to C. gloeosporioides infection, offering new insights into the genomic evolution and molecular mechanisms of poplar CBP60 .