Pepper(Capsicum annuum)xylogen-like arabinogalactan protein(XYLP)1 and XYLP2 promote synthesis of lignin during stem development to cope with stresses

Pepper stems exhibit a high level of strength and lignin deposition to support plant growth,which direct the cultivation style without binding sticks or scaffolding.However,regulation of lignin synthesis and accumulation in pepper stem has not been extensively studied.Herein,we first investigated the pepper stem developmental process and confirmed that increasing lignin accumulation occurs during stem growth.We then performed genome-wide identification and characterization of xylogen-like arabinogalactan protein(XYLP)family members and obtained 10,22,and 19 XYLPs in pepper,tomato,and potato respectively.Evaluation of the phylogenetic relationship among the identified XYLPs suggested that these proteins are conserved in Solanaceae.Thereafter,we analyzed the 10 CanXYLP genes and observed that these genes exhibit differential expressing patterns at different stages of pepper stem development.Among these genes,two XYLPs,namely CanXYLP1 and CanXYLP2,exhibited an increased expression pattern and a strong correlation with lignin accumulation in pepper stem.We further found that CanXYLP1 and CanXYLP2 play a role in pepper stem lignification by positively regulating the lignin synthesis pathway genes in pepper,and the CanXYLP1/2-silenced plants displayed a blocked lignification phenotype.Finally,we confirmed that CanXYLP1/2 expression is upregulated in response to some abiotic and biotic signals,suggesting that these two genes enhance the tolerance of pepper stem to unfavorable conditions.These results contribute to our understanding of the molecular mechanism controlling pepper stem lignification,and the relationship between the lignin content of pepper stem and XYLPs.