Transcriptome Profiling of Melaleuca quinquenervia Challenged by Myrtle Rust Reveals Differences in Defense Responses Among Resistant Individuals.

Plants have developed complex defense mechanisms to protect themselves against pathogens. A wide-host-range fungus, Austropuccinia psidii, which has caused severe damage to ecosystems and plantations worldwide, is a major threat to Australian ecosystems dominated by members of the family Myrtaceae. In particular, the east coast wetland foundation tree species Melaleuca quinquenervia, appears to be variably susceptible to this pathogen. Understanding the molecular basis of host resistance would enable better management of this rust disease. We identified resistant and susceptible individuals of M. quinquenervia and explored their differential gene expression in order to discover the molecular basis of resistance against A. psidii. Rust screening of germplasm showed a varying degree of response, with fully resistant to highly susceptible individuals. We used transcriptome profiling in samples collected before and at 5 days postinoculation (dpi). Differential gene expression analysis showed that numerous defense-related genes were induced in susceptible plants at 5 dpi. Mapping reads against the A. psidii genome showed that only susceptible plants contained fungal-derived transcripts. Resistant plants exhibited an overexpression of candidate A. psidii resistance-related genes such as receptor-like kinases, nucleotide-binding site leucine-rich repeat proteins, glutathione S-transferases, WRKY transcriptional regulators, and pathogenesis-related proteins. We identified large differences in the expression of defense-related genes among resistant individuals.

Effect of tea tree oil (Melaleuca alternifolia) on the longevity and immune response of rats infected by Trypanosoma evansi.

This study aimed to evaluate the effect of tea tree oil (TTO - Melaleuca alternifolia) on hepatic and renal functions, and the immune response of rats infected by Trypanosoma evansi. A pilot study has shown that rats treated with TTO orally (1 ml kg(-1)) had increased survival rate without curative effect. In order to verify if increased longevity was related to a better immune response against T. evansi when using tea tree oil, a second experiment was conducted. Thus, twenty-four rats were divided into four groups. The groups A and B were composed of uninfected animals, and the groups C and D had rats experimentally infected by T. evansi. Animals from the groups B and D were treated orally with TTO (1 ml kg(-1)) for three days. Blood samples were collected to verify humoral response analysis for immunoglobulins (IgA, IgM, IgE, and IgG) and cytokines (TNF-α, INF-γ, IL-1, IL-6, IL-4, and IL-10) at days 0, 3, 5 and 15 post-infection (PI). TTO treatment caused changes in the immunoglobulins and cytokines profile, as well as the course of T. evansi infection in rats. It was found that the TTO was not toxic, i.e., hepatic and renal functions were not affected. Therefore, it is possible to conclude that TTO influences the levels of inflammatory mediators and has trypanocidal effect, increasing life expectancy of rats infected by T. evansi.

Melaleuca tree and respiratory disease.

BACKGROUND: The role of Melaleuca quinquenervia tree as a source of allergen(s) and respiratory irritant(s) is controversial. OBJECTIVE: Determine whether Melaleuca tree pollen or odor is medically important. METHODS: A 2-year aeroallergen survey and skin test (ST) results of 1,017 subjects were reviewed. Sixteen subjects were selected based on positive Melaleuca pollen extract (MPE) STs. Double-blind nasal challenges with MPE were performed on six subjects. Single-blind bronchial challenges with MPE were performed on four. To evaluate the irritant effect, 11 subjects received 34 different Melaleuca odor challenges (blossoms, bark, and leaves) through a closed system for up to 30 minutes. Four inhaled an odor from cajeput oil (derived from Melaleuca leaves) for 1 hour. Spirometry was performed before and after odor challenges. Radioallergosorbent test using MPE was compared with MPE STs in 15 subjects. RESULTS: The aeroallergens survey revealed insignificant numbers of Melaleuca pollen. Ninety-seven of 1,017 subjects were a 2+ or greater intradermal MPE ST. One of 6 double-blind nasal challenges and 1 of 4 single-blind bronchial challenges using MPE were positive in subjects with positive MPE STs. All 38 odor challenges with blossoms, bark, leaves, and cajeput oil were nonreactive. The MPE radioallergosorbent test correlated with MPE ST results. CONCLUSIONS: The Melaleuca tree is not a significant source of aeroallergen. The Melaleuca odor is not a respiratory irritant. MPE antigen(s) has been shown to cross-react with pollen extracts from a proven aeroallergen (Bahia grass pollen) possibly explaining the few cases of positive MPE STs with positive nasal/bronchial challenges.