Abstract
BackgroundManganese (Mn), an essential element for plants, can be toxic when present in excess. Stylo (Stylosanthes) is a pioneer tropical legume with great potential for Mn tolerance, but its Mn tolerance mechanisms remain poorly understood.ResultsIn this study, variations in Mn tolerance were observed among nine stylo genotypes. Stylo genotype ‘RY5’ exhibited the highest Mn tolerance compared to the other tested genotypes, whereas ‘TF2001’ was a Mn-sensitive genotype. The mechanisms underlying the response of stylo to Mn toxicity were further investigated using these two genotypes with contrasting Mn tolerance. Results showed that stylo genotype RY5 exhibited Mn tolerance superior to that of genotype TF2001, showing lower reductions in leaf chlorophyll concentration, chlorophyll fluorescence parameters, photosynthetic indexes and plant dry weight under Mn toxicity. A label-free quantitative proteomic analysis was conducted to investigate the protein profiles in the leaves and roots of RY5 in response to Mn toxicity. A total of 356 differentially expressed proteins (DEPs) were identified, including 206 proteins from leaves and 150 proteins from roots, which consisted of 71 upregulated, 62 downregulated, 127 strongly induced and 96 completely suppressed proteins. These DEPs were mainly involved in defense response, photosynthesis, carbon fixation, metabolism, cell wall modulation and signaling. The qRT-PCR analysis verified that 10 out of 12 corresponding gene transcription patterns correlated with their encoding proteins after Mn exposure. Finally, a schematic was constructed to reveal insights into the molecular processes in the leaves and roots of stylo in response to Mn toxicity.ConclusionsThese findings suggest that stylo plants may cope with Mn toxicity by enhancing their defense response and phenylpropanoid pathways, adjusting photosynthesis and metabolic processes, and modulating protein synthesis and turnover. This study provides a platform for the future study of Mn tolerance mechanisms in stylo and may lead to a better understanding of the potential mechanisms underlying tropical legume adaptation to Mn toxicity.
Highlights
Manganese (Mn), an essential element for plants, can be toxic when present in excess
The results showed that SPAD values in the leaves of RY5 and TF2001 were decreased by 19.7 and 48.9% in the excess Mn treatment compared to their respective controls (Table 1)
The Fv/Fm, ΦPSII, excitation pressure of photosystem II (PSII) (1-qL) and electron transport rate (ETR) calculated from ΦPSII were declined in the two tested stylo genotypes under excess Mn conditions compared to their respective controls (Table 1)
Summary
Manganese (Mn), an essential element for plants, can be toxic when present in excess. Manganese (Mn) is the second most abundant transition metal in the Earth’s crust and is widely distributed in soils, sediments and water as well as in biological materials. Mn in trace amounts is essential for humans, animals and plants, Mn is considered a heavy metal; at excessive levels in farmlands, it decreases crop productivity and quality and threatens human health [3]. Excess Mn toxicity causes adverse impacts at various morphological levels, leading to symptoms such as chlorosis and necrosis, crinkled leaves and brown spots and, growth inhibition [5, 6]
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