Abstract
Marssonina brunnea causes a major disease that limits poplar growth. Lignin and lignan play essential roles in protecting plants from various biological stresses. Dirigent (DIR) proteins are thought to control the stereoselective coupling of coniferyl alcohol in the formation of lignan and lignin. DIR family members have been well studied in several plant species, but no previous detailed genome-wide analysis has been carried out in forest trees, such as poplar. We identified 40 PtDIR genes in Populus trichocarpa and classified them into three subgroups (DIR-a, DIR-b/d, and DIR-e) based on phylogenetic analyses. These genes are distributed on 11 poplar chromosomes, and 80% of PtDIRs (32/40) are intronless. The cis-element analysis inferred that PtDIRs possess many types of biological and abiotic stress-response cis-elements. We also analyzed intra- and inter-specific collinearity, which provided deep insights into the evolutionary characteristics of the poplar DIR genes. Analyses of the protein tertiary structure and critical amino acid residues showed that PtDIR7–10 and PtDIR13–16, which belong to the DIR-a subfamily, might be involved in the regio- and stereo-selectivity of bimolecular phenoxy radical coupling in poplars. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) analysis revealed different expression patterns for the PtDIR genes of P. trichocarpa and the PeDIR genes of ‘Nanlin 895’ in various tissues. Additionally, we analyzed responses of PeDIRs to M. brunnea and different phytohormone treatments (abscisic acid, salicylic acid, methyl jasmonate, and ethylene) in ‘Nanlin 895’. The results showed that at least 18 genes responded strongly to M. brunnea, and these PeDIRs also showed significant responses to phytohormones. These results suggest that DIR genes are involved in the poplar defense response against M. brunnea, and this study will provide fundamental insights for future research on poplar DIR genes.
Highlights
IntroductionWoody plants have a long growth cycle and are vulnerable to diseases, insect pests, and other stresses [3]
We identified 40 PtDIRs from the P. trichocarpa genome
PtDIR proteins from the DIR-a subfamily showed that PtDIR7 and could possibly catalyze the formation of (−)-pinoresinol, while PtDIR8, 9, 10, 14, and could possibly catalyze the formation of (+)-pinoresinol
Summary
Woody plants have a long growth cycle and are vulnerable to diseases, insect pests, and other stresses [3]. Poplar black spot, which is mainly caused by Marssonina brunnea is a major disease that limits poplar growth. M. brunnea infection leads to premature defoliation and seriously restricts growth [4,5,6]. It is essential to investigate M. brunnea resistance genes related to M. brunnea. Phytohormones, including abscisic acid (ABA) [7,8], salicylic acid (SA) [9], methyl jasmonate (MeJA) [4,6,10], ethylene (ETH) [6], play an important role in the process of poplar disease resistance
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
