Abstract
Breeding for drought-tolerant crops is a pressing issue due to the increasing frequency and duration of droughts caused by climate change. Although important sources of variation for drought tolerance exist in wild relatives, the mechanisms and the key genes controlling tolerance in tomato are little known. The aim of this study is to determine the drought response of the tomato wild relative Solanum pennellii (Sp) compared with the cultivated tomato Solanum lycopersicum (Sl). The paper investigates the physiological and molecular responses in leaves of Sp and Sl plants without stress and moderate drought stress. Significant physiological differences between species were found, with Sp leaves showing greater ability to avoid water loss and oxidative damage. Leaf transcriptomic analysis carried out when leaves did not as yet show visual dehydration symptoms revealed important constitutive expression differences between Sp and Sl species. Genes linked to different physiological and metabolic processes were induced by drought in Sp, especially those involved in N assimilation, GOGAT/GS cycle and GABA-shunt. Up-regulation in Sp of genes linked to JA/ET biosynthesis and signaling pathways was also observed. In sum, genes involved in the amino acid metabolism together with genes linked to ET/JA seem to be key actors in the drought tolerance of the wild tomato species.
Highlights
Most crops are susceptible to drought stress, a main environmental factor responsible for yield losses worldwide[1]
This difference in visual symptoms was due to the lower transpired water percentages in Solanum pennellii (Sp) shoots compared with Solanum lycopersicum (Sl) throughout the dehydration period (Fig. 1B), which was reflected in the significantly higher shoot water content of Sp compared with Sl at the end of cycle (3.93 ± 0.06 and 6.41 ± 0.49 mL H2O g−1 DW in Sl and Sp respectively)
In order to corroborate that the dehydration tolerance of Sp is associated to a lower water loss occurring through the leaves, we first measured leaf water loss by using detached leaves from plants grown in control condition (Fig. 1D)
Summary
Most crops are susceptible to drought stress, a main environmental factor responsible for yield losses worldwide[1]. Previous results from our group showed that one of the strategies used by S. pennellii against osmotic stress induced by salinity[22] was the avoidance of leaf dehydration by osmotic adjustment, inducing high accumulation of solutes during the stress period[23,24] This adaptation strategy appeared earlier in the time-course of drought response of S. pennellii than in cultivated tomato. The tomato wild species accumulated organic solutes as sugars and the diamine putrescine if inorganic solutes were not sufficient to reduce the osmotic potential[24,25] Another drought tolerant strategy is to limit water loss by leaf transpiration, which is used by S. pennellii under osmotic stress, as our previous results demonstrated[26,27]. We show the important constitutive gene expression differences between both species as well as the genes induced by drought stress in the tolerant species S. pennellii, which are mainly involved in amino acid metabolism and hormones
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