Transcriptome and metabolome analyses revealed the response mechanism of pepper roots to Phytophthora capsici infection.

BACKGROUND: Phytophthora root rot caused by the oomycete Phytophthora capsici is the most devastating disease in pepper production worldwide, and current management strategies have not been effective in preventing this disease. Therefore, the use of resistant varieties was regarded as an important part of disease management of P. capsici. However, our knowledge of the molecular mechanisms underlying the defense response of pepper roots to P. capsici infection is limited. METHODS: A comprehensive transcriptome and metabolome approaches were used to dissect the molecular response of pepper to P. capsici infection in the resistant genotype A204 and the susceptible genotype A198 at 0, 24 and 48 hours post-inoculation (hpi). RESULTS: More genes and metabolites were induced at 24 hpi in A204 than A198, suggesting the prompt activation of defense responses in the resistant genotype, which can attribute two proteases, subtilisin-like protease and xylem cysteine proteinase 1, involved in pathogen recognition and signal transduction in A204. Further analysis indicated that the resistant genotype responded to P. capsici with fine regulation by the Ca2+- and salicylic acid-mediated signaling pathways, and then activation of downstream defense responses, including cell wall reinforcement and defense-related genes expression and metabolites accumulation. Among them, differentially expressed genes and differentially accumulated metabolites involved in the flavonoid biosynthesis pathways were uniquely activated in the resistant genotype A204 at 24 hpi, indicating a significant role of the flavonoid biosynthesis pathways in pepper resistance to P. capsici. CONCLUSION: The candidate transcripts may provide genetic resources that may be useful in the improvement of Phytophthora root rot-resistant characters of pepper. In addition, the model proposed in this study provides new insight into the defense response against P. capsici in pepper, and enhance our current understanding of the interaction of pepper-P. capsici.

Efficacy of Sijunzi decoction on limb weakness in spleen Qi deficiency model rats through adenosine monophosphate-activated protein kinase/unc-51 like autophagy activating kinase 1 signaling.

OBJECTIVE: To investigate the efficacy of Sijunzi decoction () on limb weakness in a rat model of spleen Qi deficiency (SQD), and to study its effect on mitophagy in skeletal muscle through adenosine monophosphate-activated protein kinase (AMPK) / unc-51 like autophagy activating kinase 1 (ULK1) signaling. METHODS: SQD model rats were produced by fasting combined with forced swimming method for 15 d. After model assessment, rats were randomly divided into four groups of 10 [low/middle/high (L/M/H) Sijunzi decoction dose groups and a normal saline (S) group]. Limb holding power (HP) and body mass (BM) were measured after 2 weeks of treatment. Following euthanasia, quadriceps femoris were dissected and myofiber and mitochondrial morphology were observed by transmission electron microscopy (TEM). Mitochondrial membrane potential (MMP), adenosine triphosphatase (ATP) and reactive oxygen species (ROS) levels were determined using colorimetric methods, and immunoblot analysis of Microtubule-associated protein light chain 3 (LC3) and Sequestosome 1 (p62) was performed to monitor mitophagy and AMPK/ULK1 signaling. RESULTS: Compared with control (C) group rats, in the S group, HP was reduced, the myofiber Z line was disordered, mitochondria were scattered, and numerous vacuoles and mitophagy were observed. MMP and ATP levels were reduced, ROS levels were elevated, and LC3B expression, and p-AMPKα (Thr172)/AMPKα, p-ULK1 (Ser555)/ULK1, and p-Raptor (Ser792)/Raptor ratios were increased, while p62 expression and p-mTOR (Ser2448)/mTOR and p-ULK1 (Ser757)/ULK1 ratios were decreased. After treatment, compared with the S group, HP was improved in M and H groups but not in the L group. Mitophagy was reduced in M, H and L groups but the Z line was disordered and vacuolization remained in the L group. ATP levels were elevated in M, H and L groups, and MMPs were elevat-ed in M and H groups but not in the L group. ROS levels were decreased in M, H and L groups, as were LC3B expression and p-Raptor (Ser792)/Raptor ratios, while p62 expression and p-mTOR (Ser2448)/mTOR and p-ULK1 (Ser757)/ULK1 ratios were increased in M and H groups but not in the L group. p-AMPKα (Thr172)/AMPKα and p-ULK1 (Ser555)/ULK1 ratios were decreased in M, H and L groups. CONCLUSIONS: Sijunzi decoction improved HP, possibly by inhibiting mitophagy via suppression of AMPK/ULK1 signaling. This restored mitochondrial morphology and improved oxidative phosphorylation, which contributed to recovery of limb weakness in SQD model rats.