Comparative secretome analysis of Streptomyces scabiei during growth in the presence or absence of potato suberin.

BACKGROUND: Suberin is a recalcitrant plant biopolymer composed of a polyphenolic and a polyaliphatic domain. Although suberin contributes to a significant portion of soil organic matter, the biological process of suberin degradation is poorly characterized. It has been suggested that Streptomyces scabiei, a plant pathogenic bacterium, can produce suberin-degrading enzymes. In this study, a comparative analysis of the S. scabiei secretome from culture media supplemented or not with potato suberin was carried out to identify enzymes that could be involved in suberin degradation. METHODS: S. scabiei was grown in the presence of casein only or in the presence of both casein and suberin. Extracellular proteins from 1-, 3- and 5-day-old supernatants were analyzed by LC-MS/MS to determine their putative functions. Real-time RT-PCR was performed to monitor the expression level of genes encoding several proteins potentially involved in suberin degradation. RESULTS: The effect of suberin on the extracellular protein profile of S. scabiei strain has been analyzed. A total of 246 proteins were found to be common in the data sets from both casein medium (CM) and casein-suberin medium (CSM), whereas 124 and 139 proteins were detected only in CM or CSM, respectively. The identified proteins could be divided into 19 functional groups. Two functional groups of proteins (degradation of aromatic compounds and secondary metabolism) were only associated with the CSM. A high proportion of the proteins found to be either exclusively produced, or overproduced, in presence of suberin were involved in carbohydrate metabolism. Most of the proteins included in the lipid metabolism class have been detected in CSM. Apart from lipid metabolism proteins, other identified proteins, particularly two feruloyl esterases, may also actively participate in the breakdown of suberin architecture. Both feruloyl esterase genes were overexpressed between 30 to 340 times in the presence of suberin. CONCLUSION: This study demonstrated that the presence of suberin in S. scabiei growth medium induced the production of a wide variety of glycosyl hydrolases. Furthermore, this study has allowed the identification of extracellular enzymes that could be involved in the degradation of suberin, including enzymes of the lipid metabolism and feruloyl esterases.

Detection of potential suberinase-encoding genes in Streptomyces scabiei strains and other actinobacteria.

Streptomyces scabiei causes common scab, an economically important disease of potato tubers. Some authors have previously suggested that S. scabiei penetration into host plant tissue is facilitated by secretion of esterase enzymes degrading suberin, a lipidic biopolymer of the potato periderm. In the present study, S. scabiei EF-35 showed high esterase activity in suberin-containing media. This strain also exhibited esterase activity in the presence of other biopolymers, such as lignin, cutin, or xylan, but at a much lower level. In an attempt to identify the esterases involved in suberin degradation, translated open reading frames of S. scabiei 87-22 were examined for the presence of protein sequences corresponding to extracellular esterases of S. scabiei FL1 and of the fungus Coprinopsis cinerea VTT D-041011, which have previously been shown to be produced in the presence of suberin. Two putative extracellular suberinase genes, estA and sub1, were identified. The presence of these genes in several actinobacteria was investigated by Southern blot hybridization, and both genes were found in most common-scab-inducing strains. Moreover, reverse transcription - polymerase chain reaction performed with S. scabiei EF-35 showed that estA was expressed in the presence of various biopolymers, including suberin, whereas the sub1 gene appeared to be specifically expressed in the presence of suberin and cutin.

Productivity and Post-Harvest Fungal Resistance of Hot Pepper as Affected by Potassium Silicate, Clove Extract Foliar Spray and Nitrogen Application.

In the present study, growth and productivity of hot pepper planted in the two successive summer seasons of 2017 and 2018 were evaluated under the effect of foliar spray of variable doses of potassium silicate (PS), and clove water extract (CWE) with different rates of nitrogen (N) fertilization application. The post-harvest resistance of hot pepper fruits to Alternaria alternata fungal infection, was also evaluated. Maximum plant height was achieved with the application of the highest rates of N, PS and CWE, while the intermediate rates were sufficient to reach the maximum number of branches, the highest leaf dry matter and chlorophyll accumulation. Fruit yield progressively increased with increasing the applied N rate. The foliar application of PS and CWE exerted a limited, yet positive effect on fruit yield. Generally, the least amount of fruit yield, amounting to 18.84 and 18.00 t ha-1, resulted from the application of the lowest N rate (144 kg ha-1) in the absence of PS and CWE. The highest significant fruit yield, amounting to 31.71 and 31.22 t ha-1, for 2017 and 2018, respectively, accompanied the application of the maximum levels of the three factors. The application of high N rates increased the post-harvest Alternaria fruit rot severity. The positive effect of CWE application in counterbalancing the negative effects associated with the high rates of N and PS may be related to the presence of phenolic and flavonoid compounds ellagic acid, benzoic acid, catechol gallic acid, rutin, myricetin, quercetin, apigenin and kaempferol as identified by High Performance Liquid Chromatography (HPLC).