COMT1 Silencing Aggravates Heat Stress-Induced Reduction in Photosynthesis by Decreasing Chlorophyll Content, Photosystem II Activity, and Electron Transport Efficiency in Tomato.

Golam J Ahammed,Wen Xu,Airong Liu,Shuangchen Chen

doi:10.3389/fpls.2018.00998

Abstract

Despite a range of initiatives to reduce global carbon emission, the mean global temperature is increasing due to climate change. Since rising temperatures pose a serious threat of food insecurity, it is important to further explore important biological molecules that can confer thermotolerance to plants. Recently, melatonin has emerged as a universal abiotic stress regulator that can enhance plant tolerance to high temperature. Nonetheless, such regulatory roles of melatonin were unraveled mainly by assessing the effect of exogenous melatonin on plant tolerance to abiotic stress. Here, we generated melatonin deficient tomato plants by silencing of a melatonin biosynthetic gene, CAFFEIC ACID O-METHYLTRANSFERASE 1 (COMT1), to unveil the role of endogenous melatonin in photosynthesis under heat stress. We examined photosynthetic pigment content, leaf gas exchange, and a range of chlorophyll fluorescence parameters. The results showed that silencing of COMT1 aggravated heat stress by inhibiting both the light reactions and the carbon fixation reactions of photosynthesis. The photosynthetic pigment content, light absorption flux, trapped energy flux, energy dissipation, density of active reaction center per photosystem II (PSII) cross-section, the photosynthetic electron transport rate, the maximum photochemical efficiency of PSII photochemistry, and the rate of CO2 assimilation all decreased in COMT1-silenced plants compared with that of non-silenced plants particularly under heat stress. However, exogenous melatonin alleviated heat-induced photosynthetic inhibition in both genotypes, indicating that melatonin is essential for maintaining photosynthetic capacity under stressful conditions. These findings provide genetic evidence on the vital role of melatonin in photosynthesis and thus may have useful implication in horticultural crop management in the face of climate change.

Highlights

Despite a range of initiatives to reduce global carbon emission, the mean global temperature is increasing over time due to climate change
Since exogenous melatonin showed a protective role against heat stress (Qi et al, 2018), we intended to unveil the role of endogenous melatonin in plant tolerance to heat stress
The contents of Chlorophyll a (Chl a), chlorophyll b (Chl b), and carotenoids were not altered by heat stress in tobacco rattle virus (TRV) control plants, heat stress significantly decreased the Chl a, Chl b, and carotenoids contents in TRV-CAFFEIC ACID O-METHYLTRANSFERASE 1 (COMT1) plants compared with that in heat-stressed TRV plants

Summary

Introduction

Despite a range of initiatives to reduce global carbon emission, the mean global temperature is increasing over time due to climate change. The occurrences of drought and heat events have become more prevalent in recent times, which pose a serious threat to global food security (Field et al, 2014). Heat stress causes water loss in aerial plant parts and impairs membrane integrity (Li et al, 2015; Li H. et al, 2016). Both photosystems I and II (PSI and PSII) are affected by heat stress due to the heat-induced inhibition of light energy absorption, energy distribution, and electron transport (Li H. et al, 2016). Since heat stress poses a serious threat to global food security, it is important to further explore key biological molecules that can mediate thermotolerance in plants

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Conclusion