Insights Into the Mechanisms Implicated in Pinus pinaster Resistance to Pinewood Nematode

Pine wilt disease (PWD), caused by the plant–parasitic nematode Bursaphelenchus xylophilus, has become a severe environmental problem in the Iberian Peninsula with devastating effects in Pinus pinaster forests. Despite the high levels of this species' susceptibility, previous studies reported heritable resistance in P. pinaster trees. Understanding the basis of this resistance can be of extreme relevance for future programs aiming at reducing the disease impact on P. pinaster forests. In this study, we highlighted the mechanisms possibly involved in P. pinaster resistance to PWD, by comparing the transcriptional changes between resistant and susceptible plants after infection. Our analysis revealed a higher number of differentially expressed genes (DEGs) in resistant plants (1,916) when compared with susceptible plants (1,226). Resistance to PWN is mediated by the induction of the jasmonic acid (JA) defense pathway, secondary metabolism pathways, lignin synthesis, oxidative stress response genes, and resistance genes. Quantification of the acetyl bromide-soluble lignin confirmed a significant increase of cell wall lignification of stem tissues around the inoculation zone in resistant plants. In addition to less lignified cell walls, susceptibility to the pine wood nematode seems associated with the activation of the salicylic acid (SA) defense pathway at 72 hpi, as revealed by the higher SA levels in the tissues of susceptible plants. Cell wall reinforcement and hormone signaling mechanisms seem therefore essential for a resistance response.

Transcriptomic analysis of cork during seasonal growth highlights regulatory and developmental processes from phellogen to phellem formation

The phellogen or cork cambium stem cells that divide periclinally and outwardly specify phellem or cork. Despite the vital importance of phellem in protecting the radially-growing plant organs and wounded tissues, practically only the suberin biosynthetic process has been studied molecularly so far. Since cork oak (Quercus suber) phellogen is seasonally activated and its proliferation and specification to phellem cells is a continuous developmental process, the differentially expressed genes during the cork seasonal growth served us to identify molecular processes embracing from phellogen to mature differentiated phellem cell. At the beginning of cork growth (April), cell cycle regulation, meristem proliferation and maintenance and processes triggering cell differentiation were upregulated, showing an enrichment of phellogenic cells from which phellem cells are specified. Instead, at maximum (June) and advanced (July) cork growth, metabolic processes paralleling the phellem cell chemical composition, such as the biosynthesis of suberin, lignin, triterpenes and soluble aromatic compounds, were upregulated. Particularly in July, polysaccharides- and lignin-related secondary cell wall processes presented a maximal expression, indicating a cell wall reinforcement in the later stages of cork formation, presumably related with the initiation of latecork development. The putative function of relevant genes identified are discussed in the context of phellem ontogeny.

Phenylpropanoids Are Connected to Cell Wall Fortification and Stress Tolerance in Avocado Somatic Embryogenesis

Somatic embryogenesis (SE) is a valuable model for understanding the mechanism of plant embryogenesis and a tool for the mass production of plants. However, establishing SE in avocado has been complicated due to the very low efficiency of embryo induction and plant regeneration. To understand the molecular foundation of the SE induction and development in avocado, we compared embryogenic (EC) and non-embryogenic (NEC) cultures of two avocado varieties using proteomic and metabolomic approaches. Although Criollo and Hass EC exhibited similarities in the proteome and metabolome profile, in general, we observed a more active phenylpropanoid pathway in EC than NEC. This pathway is associated with the tolerance of stress responses, probably through the reinforcement of the cell wall and flavonoid production. We could corroborate that particular polyphenolics compounds, including p-coumaric acid and t-ferulic acid, stimulated the production of somatic embryos in avocado. Exogen phenolic compounds were associated with the modification of the content of endogenous polyphenolic and the induction of the production of the putative auxin-a, adenosine, cellulose and 1,26-hexacosanediol-diferulate. We suggest that in EC of avocado, there is an enhanced phenylpropanoid metabolism for the production of the building blocks of lignin and flavonoid compounds having a role in cell wall reinforcement for tolerating stress response. Data are available at ProteomeXchange with the identifier PXD019705.

Comparative genome analysis of Bacillus okhensis Kh10-101T reveals insights into adaptive mechanisms for halo-alkali tolerance

Background: Bacillus okhensis, isolated from saltpan near port of Okha, India, was initially reported to be a halo-alkali tolerant bacterium.We previously sequenced it’s 4.86 Mb genome, here we analyze its genome and physiological responses to high salt and high pH stress. Results: B. okhensis is a halo-alkaliphile with optimal growth at pH 10 and 5% NaCl. 16S rDNA phylogenetic analysis resulted in habitat based segregation of 106 Bacillus species into 3 major clades with all alkaliphiles in one clade clearly suggesting a common ancestor for alklaliphilic Bacilli. We observed that B. okhensis has been adapted to survive at halo-alkaline conditions, by acidification of surrounding medium using fermentation of glucose to organic acids. Comparative genome analysis revealed that the surface proteins which are exposed to external high pH environment of B. okhensis were evolved with relatively higher content of acidic amino acids than their orthologues of B. subtilis. It posess relatively more genes involved in the metabolism of osmolytes and sodium dependent transporters in comparison to B. subtilis. Growth of B. okhensis is Na+ dependent, with a minimum requirement of 4% NaCl at neutral pH but 0.5% NaCl is enough at pH 10. It tolerated sudden increase of salt concentration of its medium, and exhibited an elongated cellular phenotype. But, could not tolerate a sudden shift of pH from 7 to 11, and cell envelope got damaged, confirming the pH regulation through cell wall reinforcement is key to survival at high-pH condition. We observed that hydroxyl ions damage the cell, but not Na+ ions, becuase at high pH Na+ ions were not accumulated inside. Conclusion: B. okhensis uses acidification of the external medium and pH dependent cell wall reinforcement to survive sodic environments. Interestingly, its growth is highly Na+ dependent and the genome encodes for a high proportion of acidic amino acids in majority of surface proteins in comparison to their orthologues of B. subtilis, a direct evidence of adaptive evolution.

Evaluation of cell wall reinforcement in feather keratin-treated waterlogged wood as imaged by synchrotron X-ray microtomography (μXRT) and TEM

Archaeological waterlogged woods (WLW) become considerably fragile over time because of chemical hydrolysis and the deterioration by microorganisms in the wet buried environment. The methods are sought for the dimensional stabilization of such woods. In the present article, the conservation of archaeological WLW of Chamaecyparis pisifera (Sieb. et Zucc.) Endl. by means of a commercially available feather keratin was in focus. The impregnation of an ancient wood from the 9th century A.D. was examined by the noninvasive synchrotron X-ray microtomography, which is well suited for imaging fragile samples. The thickness of the cell walls of keratin-treated wood was preserved and was comparable with that of recent wood. Notably, the middle lamella (ML) of keratin-treated wood appeared to be electron dense as indicated by transmission electron microscopy. Thus, it can be concluded that feather keratin is predominantly adsorbed on the ML and it prevents wood cell walls from collapsing and provides reinforcement.