Protein Profiling of Psittacanthus calyculatus during Mesquite Infection

Abstract

Psittacanthus calyculatus is a hemiparasite mistletoe that represents an ecological problem due to the impacts caused to various tree species of ecological and commercial interest. Although the life cycle for the Psittacanthus genus is well established in the literature, the development stages and molecular mechanism implicated in P. calyculatus host infection are poorly understood. In this study, we used a manageable infestation of P. laevigata with P. calyculatus to clearly trace the infection, which allowed us to describe five phenological infective stages of mistletoe on host tree branches: mature seed (T1), holdfast formation (T2), haustorium activation (T3), haustorium penetration (T4), and haustorium connection (T5) with the host tree. Proteomic analyses revealed proteins with a different accumulation and cellular processes in infective stages. Activities of the cell wall-degrading enzymes cellulase and β-1,4-glucosidase were primarily active in haustorium development (T3), while xylanase, endo-glucanase, and peptidase were highly active in the haustorium penetration and xylem connection (T4). Patterns of auxins and cytokinin showed spatial concentrations in infective stages and moreover were involved in haustorium development. These results are the first evidence of proteins, cell wall-degrading enzymes, and phytohormones that are involved in early infection for the Psittacanthus genus, and thus represent a general infection mechanism for other mistletoe species. These results could help to understand the molecular dialogue in the establishment of P. calyculatus parasitism.

Extracellular Self- and Non-Self DNA Involved in Damage Recognition in the Mistletoe Parasitism of Mesquite Trees

“…However, phosphorylation of MAPKs is one of the first reactions that cells have to DAMP sensing [ 106 ]. exDNA is recognized by surface proteins known as pattern-recognition receptors (PRRs), which sets off immune responses such as Ca 2+ ion fluxes across the plasma membrane, the production of ROS, the activation of MAPKs, and a quicker regulation of defensive gene expression [ 19 , 24 , 41 , 43 , 47 , 58 , 99 ] to phosphorylate NADPH oxidases (NOX family) to produce O 2 •− in the apoplast, initiating the oxidative burst within a few minutes [ 107 ]. Based on the above, the application of self-exDNA as a damage-specific DAMP strongly induces MAPK regulation in mesquite trees.…”

“…The infective process takes place during seed germination, and the appearance of a prehaustorium occurs which activates the expression of genes encoding an arsenal of cell-wall-degrading enzymes that help to breach the host bark and the cortex [ 19 ]. Through mechanical pressure, the haustorium penetrates the branch and will connect with the xylem host [ 19 ]. The host experiences mechanical wounding during this penetration process, and the haustorium tissue may also experience mechanical wounding as a result of friction between the branch’s woody walls due to the narrow process inside the branch.…”

“…In addition, transcriptome analysis in the infective process of Psittacanthus schiedeanus mistletoe, an arsenal of cell-wall-degrading enzymes like glucosyl hydrolases is necessary for the host infection [ 116 ]. Similarly, enzymatic analyses in P. calyculatus mistletoe revealed high activities of cell-wall-degrading enzymes such as cellulase and β-1,4-glucosidase that were primarily active in haustorium development, while xylanase and endo-glucanase were highly active in the haustorium penetration and xylem connection [ 19 ]. Additionally, we found that the host reacts against P. calyculatus mistletoe by producing oxidative stress processes like H 2 O 2 , ROS-related enzymes, and different concentrations of phytohormones like JA and SA [ 117 ].…”

“…However, phosphorylation of MAPKs is one of the first reactions that cells have to DAMP sensing [106]. exDNA is recognized by surface proteins known as pattern-recognition receptors (PRRs), which sets off immune responses such as Ca 2+ ion fluxes across the plasma membrane, the production of ROS, the activation of MAPKs, and a quicker regulation of defensive gene expression [19,24,41,43,47,58,99] to phosphorylate NADPH oxidases (NOX family) to produce O 2…”

“…While sufficient information exists regarding the pollination syndromes that P. calyculatus uses to attract and manipulate pollinators and visitors [ 18 ], the molecular mechanisms of the infection process remain unknown. Currently, it is well-known that seeds that birds deposit on branches can germinate, leading to the haustorium tissue formation, and the emergence of this intrusive organ is accompanied by high activity of cell-wall-degrading enzymes [ 19 ]. The enzymatic degradation of the host bark causes a pit on the surface, that functions as an anchor for the haustorium penetration.…”