Abstract
Vacuolar water movement is largely controlled by membrane channels called tonoplast-intrinsic aquaporins (TIP-AQPs). Some TIP-AQP genes, such as TIP2;2 and TIP1;1, are up-regulated upon exposure to biotic stress. Moreover, TIP1;1 transcript levels are higher in leaves of a tomato (Solanum lycopersicum) line resistant to Tomato yellow leaf curl virus (TYLCV) than in those of a susceptible line with a similar genetic background. Virus-induced silencing of TIP1;1 in the tomato resistant line and the use of an Arabidopsis (Arabidopsis thaliana) tip1;1 null mutant showed that resistance to TYLCV is severely compromised in the absence of TIP1:1. Constitutive expression of tomato TIP2;2 in transgenic TYLCV-susceptible tomato and Arabidopsis plants was correlated with increased TYLCV resistance, increased transpiration, decreased abscisic acid levels, and increased salicylic acid levels at the early stages of infection. We propose that TIP-AQPs affect the induction of leaf abscisic acid, which leads to increased levels of transpiration and gas exchange, as well as better salicylic acid signaling.
Highlights
Plants manage their water balance in different ways
We propose that Tonoplast intrinsic proteins (TIPs)-AQPs affect the induction of leaf abscisic acid (ABA), which leads to increased levels of transpiration and gas exchange, as well as better salicylic acid (SA) signaling
The results presented here indicate that TIP-AQPs are involved in Tomato yellow leaf curl virus (TYLCV) resistance, which is controlled by cellular water balance and transpiration, with subsequent effects on hormonal balance and sugar signaling
Summary
Plants manage their water balance in different ways. Some plants maintain a strict transpiration rate, ensuring nearly constant leaf water potential and relative water content; this conservative strategy is referred to as isohydric. This switch was accompanied by increased transpiration and fruit set under mild to moderate (but not severe) drought conditions (Sade et al, 2009). It has been postulated that the genes that are expressed at higher levels in R plants (as compared to S plants) are related to resistance and that silencing these genes will lead to the collapse of resistance (Eybishtz et al, 2009) This concept has been verified for a number of genes, including the tomato hexose transporter LeHT1 (Sade et al, 2012a; Eybishtz et al, 2010).
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