Browsing by Author "Warren, Kyle"

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    Is AtGSTF2 involved in lumichrome perception and transport?
    (Stellenbosch : Stellenbosch University, 2024-03) Warren, Kyle; Hills, Paul Norman; Stellenbosch University. Faculty of AgriSciences. Department of Genetics & Institute of Plant Biotechnology.
    ENGLISH ABSTRACT: A number of exudates from plant growth-promoting rhizobacteria (PGPR) have been increasingly studied and used as an alternative way of promoting plant health and growth. One such exudate is lumichrome, a signal molecule which has been shown to elicit a growth response across multiple species. Recent studies have identified some of the molecular mechanisms which underpin this growth response, however, to date it remains unknown how lumichrome is perceived and transported in planta. It was proposed that the Arabidopsis Glutathione S-Transferase (GST) AtGSTF2 may act as either a receptor or a transporter of lumichrome, as a previous study had found lumichrome was able to bind to AtGSTF2 with high affinity when the Arabidopsis gene was overexpressed in Escherichia coli. Consequently, AtGSTF2 overexpressor (OE) and knockout (KO) lines were generated in Arabidopsis thaliana to test whether these lines would show enhancements or reductions in the growth effects of lumichrome, and to gain additional insight into the role of AtGSTF2 in Arabidopsis. It was determined that overexpression of AtGSTF2 did not affect the growth response of treated plants to lumichrome, although it was found that the OE plants had increased overall plant growth and differences in a number of physiological responses in comparison to untreated wild-type plants. Previous studies had shown no obvious phenotypic effects from AtGSTF2 overexpression under normal growth conditions, although the plants had increased tolerance to phenolic stress; however, this study showed that overexpression of AtGSTF2 resulted in an increase in both fresh and dry biomass, an increase in the number of leaves, increased starch and sugar levels, as well as higher stomatal conductance and transpiration rates than wild-type plants. However, in both OE lines generated, lumichrome treatment reduced plant biomass, whilst leaf number was also reduced following lumichrome treatment in one of the two OE lines. RT-qPCR analysis showed decreased expression of AtGSTF2 in wild-type plants following lumichrome treatment, however, increased expression compared to wild-type controls was seen in growth-related genes XTH9 and CYCA1 and the jasmonate-related gene JAL34. However, lumichrome-treatment of OE plants resulted in significant differences in expression patterns for the lumichrome- responsive genes studied compared to its effects on the transcripts in wild-type plants, as the overexpression of AtGSTF2 appeared to decrease ACO1 and CYCA1 expression. Overexpression of AtGSTF2 increased plant growth in comparison to the wild-type plants, suggesting that AtGSTF2 plays a critical role in development. In summary, the evidence from this study revealed no correlations between lumichrome-related growth or gene expression responses and AtGSTF2 expression, suggesting that AtGSTF2 is most likely not involved in either lumichrome perception or transport. Despite being one of the most widely studied phi-class GSTs, little is known about the functions of AtGSTF2. This study proposes that AtGSTF2 plays a more important role in plant growth than previously thought, and it is recommended that future studies should focus on the role of AtGST2 in plant growth and development.