No abstract

Clematis species are commonly grown in western and Japanese gardens. Heat stress can inhibit many physiological processes mediating plant growth and development. The mechanism regulating responses to heat has been well characterized in Arabidopsis thaliana and some crops, but not in horticultural plants, including Clematis species. In this study, we found that Clematis alpina 'Stolwijk Gold' was heat-sensitive whereas Clematis vitalba and Clematis viticella 'Polish Spirit' were heattolerant based on the physiological analyses in heat stress. Transcriptomic pro ling identi ed a set of heat tolerance-related genes (HTGs). Consistent with the observed phenotype in heat stress, 41.43% of the differentially expressed HTGs between heat treatment and control were down-regulated in heat-sensitive cultivar Stolwijk Gold, but only 9.80% and 20.79% of the differentially expressed HTGs in heat resistant C. vitalba and Polish Spirit, respectively. Co-expression network, protein-protein interaction network and phylogenetic analysis revealed that the genes encoding heat shock transcription factors (HSFs) and heat shock proteins (HSPs) played an essential role in Clematis resistance to heat stress. Ultimately, we proposed that two clades of HSFs may have diverse functions in regulating heat resistance from C. vitalba and CvHSFA2-2 could endow different host with high temperature resistance. This study provides rst insights into the diversity of the heat response mechanisms among Clematis species.

Background: Clematis species are commonly grown in western and Japanese gardens. Heat stress can inhibit many physiological processes mediating plant growth and development. The mechanism regulating responses to heat has been well characterized in Arabidopsis thaliana and some crops, but not in horticultural plants, including Clematis species. Results: In this study, we identified a heat-sensitive Clematis variety (Clematis alpina ‘Stolwijk Gold’) and two heat-tolerant Clematis varieties (Clematis vitalba and Clematis viticella ‘Polish Spirit’) based on heat-related physiological indices. The leaf transcriptomes under normal and heat stress conditions were analyzed by RNA sequencing. Additionally, heat tolerance-related genes (HTGs) were identified and their expression levels were analyzed. Following heat treatments, 41.67% of the differentially expressed HTGs in Stolwijk Gold had down-regulated expression levels, whereas only 9.80% and 21.36% of the differentially expressed HTGs in C. vitalba and Polish Spirit, respectively, had the same trend. The HTGs’ co-expression and protein–protein interaction networks revealed that the hub genes regulating Clematis resistance to heat stress encode heat shock transcription factors (HSFs) and heat shock proteins (HSPs). Moreover, the sensitivity of Stolwijk Gold to heat is mainly due to the heat-induced down-regulated expression of these genes. On the basis of phylogenetic and expression analyses, the differentially expressed HSF and HSP genes in the three examined varieties were divided into three and four clades, respectively, with similar expression profiles common among orthologous family members. Furthermore, we identified two HSF classes in C. vitalba that may have diverse functions influencing heat resistance. Conclusions: Our study provides insights into the diversity of the heat response mechanisms among Clematis species and may be useful for breeding new heat-resistant ornamental Clematis varieties.