6-deoxy-6-amino chitosan: A plant defence priming biopolymer that enhances resistance against Botrytis cinerea in tomato and Fusarium verticillioides in maize

Moola, Naadirah

6-deoxy-6-amino chitosan: A plant defence priming biopolymer that enhances resistance against Botrytis cinerea in tomato and Fusarium verticillioides in maize

Thesis / Dissertation

2024

Abstract

Aminochitosan, derived from chitosan, features enhanced water solubility, and improved antifungal efficacy attributed to an additional amine group at the C-6 position, hinting at its superior antifungal potential compared to native chitosan. This PhD thesis aimed to explore the optimal concentration of aminochitosan and its molecular weight fractions for enhanced antifungal and priming properties in the tomato/Botrytis cinerea and maize/ Fusarium verticillioides pathosystems. In the B. cinerea pathosystem, various concentrations of aminochitosan were assessed for their antifungal effectiveness against B. cinerea growth and sporulation. Additionally, in planta studies were conducted to phenotype and quantify temporal stress responses using both qualitative and quantitative chlorophyll fluorescence imaging as well as DAB assays combined with microscopy. Despite batch-to-batch variations, aminochitosan consistently inhibited fungal growth and sporulation in a dose-dependent manner. In planta, aminochitosan pre-treatment induced robust defence responses in tomato leaves, resulting in a resistant phenotype that was mediated through a combination of enhanced photosynthetic efficiency as evidenced by enhanced Fv/Fm and chlorophyll content. The DAB assays suggested that these resistant phenotypes were also ROS-independent (H2O2 specifically) due to the strong positive impact of direct inhibition. The resistant phenotype and optimal efficacy of the aminochitosan MW fractions was observed at 3.5-15 kDa for antifungal efficacy and 15-20 kDa for in planta efficacy. Consequently, leaf senescence, hypersensitive responses and therefore necrosis were mitigated suggesting that aminochitosan primed defence responses in both mock and B. cinerea inoculated leaves. A temporal, label-free quantitative proteomic analysis revealed the differential priming of key molecular mechanisms underpinning aminochitosan primed states both with and without B. cinerea infection at 6 and 9 hpi in the tomato/B. cinerea pathosystem. Aminochitosan treatment (1 mg/mL) differentially regulated proteins as early as 6 hpi with some of the induced responses being sustained up to 9 hpi. Additionally, several proteins were oppositely regulated between aminochitosan pre-treatment and B. cinerea infection, indicating differential regulation patterns between the “primed state” and the “triggered state”. The proteomic data therefore partially validated the ‘priming' capacity of aminochitosan in 5- week-old tomato leaves, specifically diamino 3 when used as a foliar spray at a concentration of 1 mg/mL. The bimodal effects of aminochitosan in a maize/Fusarium verticillioides pathosystem were investigated by assessing the direct antifungal efficacy and elicitation of plant defence properties in planta. Aminochitosan displayed significant antifungal activity on both radial growth and sporulation at a minimum concentration of 1 mg/mL. Aminochitosan was also assessed in planta as preventative or curative treatments in maize seedlings infected with F. verticillioides at two time points. In the preventative treatment, salicylic acid accumulated during the early stages of infection (biotrophic phase) whereas in the curative treatment, jasmonic acid accumulated during the necrotrophic phase. In summary, we demonstrated that water-soluble aminochitosan possesses key properties that enable plant priming in addition to its superior direct antifungal activity compared to native chitosan. We also identified the optimal molecular weights and concentrations necessary for achieving maximum and 50% inhibition activity

Keywords

Molecular and Cell Biology

Reference:

Collections

PhD / Doctoral

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