Phytophthora capsici infection causes dynamic alterations in tRNA modifications and their associated gene candidates in black pepper.

The efforts to signify the relevance of tRNA modifications were always within the limits of prokaryotes, humans, and some fewer model plant systems. The story of tRNA modifications in higher plants is still overlooked, especially in non-model spice crops. Stress causes alterations in tRNA modifications to facilitate the downstream functions of tRNAs. The present study was done to identify and better understand the fate of tRNA nucleoside modifications during biotic stress response in a widely used spice crop called Black pepper. We have uncovered the various tRNA nucleoside modifications present in black pepper. Methylations were the predominant nucleoside modifications in black pepper tRNAs. Furthermore, the different methyltransferase gene candidates implicated in catalyzing tRNA nucleoside methylations in black pepper were also identified. The LC-MS profile showed that certain tRNA nucleoside modifications showed varied abundance upon P. capsici infection. The N4-acetylcytidine (ac4C) nucleoside modification has shown a constant hike at 24 and 48 hpi. At the same time, some nucleoside modifications have exhibited a time-dependent abundance. Altogether our study suggests that tRNA modifications and the expression of associated enzymes are altered during biotic stress regulation.

Non-Targeted Metabolite Profiling Reveals Host Metabolomic Reprogramming during the Interaction of Black Pepper with Phytophthora capsici.

Phytophthora capsici is one of the most destructive pathogens causing quick wilt (foot rot) disease in black pepper (Piper nigrum L.) to which no effective resistance has been defined. To better understand the P. nigrum-P. capsici pathosystem, we employed metabolomic approaches based on flow-infusion electrospray-high-resolution mass spectrometry. Changes in the leaf metabolome were assessed in infected and systemic tissues at 24 and 48 hpi. Principal Component Analysis of the derived data indicated that the infected leaves showed a rapid metabolic response by 24 hpi whereas the systemic leaves took 48 hpi to respond to the infection. The major sources of variations between infected leaf and systemic leaf were identified, and enrichment pathway analysis indicated, major shifts in amino acid, tricarboxylic acid cycle, nucleotide and vitamin B6 metabolism upon infection. Moreover, the individual metabolites involved in defensive phytohormone signalling were identified. RT-qPCR analysis of key salicylate and jasmonate biosynthetic genes indicated a transient reduction of expression at 24 hpi but this increased subsequently. Exogenous application of jasmonate and salicylate reduced P. capsici disease symptoms, but this effect was suppressed with the co-application of abscisic acid. The results are consistent with abscisic acid reprogramming, salicylate and jasmonate defences in infected leaves to facilitate the formation of disease. The augmentation of salicylate and jasmonate defences could represent an approach through which quick wilt disease could be controlled in black pepper.