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Research: TYLCV promotes plant tolerance to drought

23/02/2022

François-Xavier Branthôme
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A growing body of research points to a positive interplay between viruses and plants. Tomato yellow curl virus (TYLCV) is able to protect tomato host plants against extreme drought. To envisage the use of virus protective capacity in agriculture, TYLCV-resistant tomato lines have to be infected first with the virus before planting.
Such virus-resistant tomato plants contain virus amounts that do not cause disease symptoms, growth inhibition, or yield loss, but are sufficient to modify the metabolism of the plant, resulting in improved tolerance to drought. This phenomenon is based on the TYLCV-dependent stabilization of amounts of key osmoprotectants induced by drought (soluble sugars, amino acids, and proteins).

 The ability of viruses to protect the infected plant hosts from negative effects of different environmental stresses is a topic that is becoming increasingly important in agricultural research. Undoubtedly, many viruses encountered in agricultural systems are pathogenic and affect yields; nonetheless, viruses may also co-exist with plants \without harming them, and even benefit to them. Some viruses are clearly beneficial to their infected host protecting them from heat and/or water scarcity. Increasing amounts of studies demonstrated the way viruses manage to increase the plant's response to environmental stresses. For example, four different RNA viruses, brome mosaic virus (BMV), cucumber mosaic virus (CMV), tobacco mosaic virus (TMV), and tobacco rattle virus (TRV), were shown to improve the infected plant's tolerance to drought. Examples of plant beneficial trade-off from infection with potato virus X {PVX) and plum pox virus (PPV) was described for Nicotiana benthamiana and Arabidopsis grown under drought conditions. Virus infection enhanced plant tolerance to drought by increasing salicylic acid amounts, in an abscisic acid (ABA)-independent manner. Tobacco rattle virus (TRV) was shown to change the stress response of Arabidopsis to low temperature; PVX – to increased environmental oxidation in N. benthamiana.

In a previous study, researchers demonstrated the ability of TYLCV infection to enhance the survival to drought of TYLCV-susceptible tomatoes. The main purpose of the current study was to compare the behavior of TYLCV-susceptible (S-967) with TYLCV-resistant (R-GF967) tomato lines grown upon water withholding. Researchers predicted that the presence of the virus in the resistant R-GF967 tomatoes would cause a similar level of protection against drought, remain symptomless, and yield (contrary to the infected susceptible tomatoes S-967 who will decay upon drought).
Indeed, viral infection of R-GF967 tomatoes caused an improvement in growth and survival. Drought did not lead to the collapse of RVD plants grown in the Jordan valley and in the greenhouse. RVD plants showed mild wilting and leaf yellowing only after 18 drought days. It must be mentioned that virus infection significantly improved drought tolerance of S-967 (SVD) tomatoes as well/ which confirmed our previous results
The capacity of plants to resist numerous environmental stresses is associated with the increase in different cellular osmoprotectants. The levels of protective sugars and ammo acids in tomato leaves improved upon drought in non-infected R-GF967 (R0D) compared to S-967 (S0D). Moreover, the patterns of most osmoprotectants analyzed, including HSPs (heat shock proteins) were more stable in R0D tomatoes, rather than in S0D tomatoes. Protein homeostasis was maintained longer in TYLCV-resistant tomatoes than in susceptible tomatoes exposed to stresses, In the current study, in addition to HSPs, the well-balanced homeostasis of R0D plants was confirmed by the enhanced stability of such osmolytes as amino acids and soluble sugars.

TYLCV infection induces drought tolerance in TYLCV-susceptible tomatoes, S-967 line in this study, and in the tomato commercial cultivar Ikram. Moreover, this study showed that the induction of drought tolerance is particularly pronounced in infected TYLCV-resistant plants (RGF967), which accumulate less amounts of virus than susceptible plants, thus not affecting plant growth and development. Findings showed that stress-protective soluble sugars and amino acids in the leaves of uninfected, and especially in virus-infected RGF967 tomatoes, resulted in the development of a buffering state, resulting in plant protection against drought during a prolonged time (Figure 1). Therefore, we propose that the establishment of stress osmoprotectant stability is the main feature underlaying increased drought tolerance of TYLCV-resistant tomatoes, which is utterly improved by virus infection.
 

The main goal of farmers all around the world is to obtain high yields. In the current study, scientists showed that the use of TYLCV-infected and TYLCV-resistant tomatoes could overcome relatively long (at least 18 drought days) periods of extreme drought, survive, and produce fruits after recovery (Figure 5). They have explored a concept based on the two apparent contradictions: on the one hand, extreme drought ultimately causes plant death; and on the other hand, TYLCV mitigates tomato disease to create a proper environment for its successful replication, allowing the plant to grow without irreversible damage.
Cultivating infected R-GF967 (or resistant cultivars similar to GF967) in conditions of water deficit is advantageous; TYLCV protects them from stress and does not interfere with their normal development. Thus, taking advantage of some of the virus effects, one can envisage cultivating TYLCV-infected and TYLCV-resistant plants in countries where drought is an acute problem.

Some complementary data
Read the complete research at www.researchgate.net.

Shteinberg, Moshik & Mishra, Ritesh & Anfoka, Ghandi & Altaleb, Miassar & Brotman, Yariv & Moshelion, Menachem & Gorovits, Rena & Czosnek, Henryk. (2021). Tomato Yellow Leaf Curl Virus (TYLCV) Promotes Plant Tolerance to Drought. Cells. 10. 2875. 10.3390/cells10112875.

Sources: hortidaily.com, researchgate.net