Ethylene and Abscisic Acid Signaling Pathways Differentially Influence Tomato Resistance to Combined Powdery Mildew and Salt Stress

Abstract

There is currently limited knowledge on the role of hormones in plants responses to combinations of abiotic and pathogen stress factors. This study focused on the response of tomato near-isogenic lines (NILs) that carry the Ol-1, ol-2, and Ol-4 loci, conferring resistance to tomato powdery mildew (PM) caused by Oidium neolycopersici, to combined PM and salt stress. These NILs were crossed with the notabilis (ABA-deficient), defenceless1 (JA-deficient), and epinastic (ET overproducer) tomato mutants to investigate possible roles of hormone signaling in response to combined stresses. In the NILs, marker genes for hormonal pathways showed differential expression patterns upon PM infection. The epinastic mutation resulted in breakdown of resistance in NIL-Ol-1 and NIL-ol-2. This was accompanied by reduced callose deposition, and was more pronounced under combined salt stress. The notabilis mutation resulted in H2O2 overproduction and reduced susceptibility to PM in NIL-Ol-1 under combined stress, but lead to higher plant growth reduction under salinity and combined stress. Resistance in NIL-ol-2 was compromised by the notabilis mutation, which was potentially caused by reduction of callose deposition. Under combined stress the compromised resistance in NIL-ol-2 was restored. PM resistance in NIL-Ol-4 remained robust across all mutant and treatment combinations. Hormone signaling is critical to the response to combined stress and PM, in terms of resistance and plant fitness. ABA appears to be at the crossroads of disease susceptibility/senescence and plant performance under combined stress These gained insights can aid in narrowing down targets for improving crop performance under stress combinations.

Plant behaviour under combined stress: tomato responses to combined salinity and pathogen stress

“…When ET was overproduced in an NIL with the epinastic mutation, the Ol‐1 based resistance was decreased, and even completely compromised under combined salt‐PM stress. Strikingly, both senescence and cell death were completely absent in Ol‐1 x epi plants under combined salt‐PM stress (Kissoudis et al ., ). This finding is contradictory to studies showing that ethylene stimulates senescence and ROS production (Bartoli et al ., ; Penfold and Buchanan‐Wollaston, ).…”

“…The increase in H 2 O 2 accumulation and callose deposition under combined stress could explain the partially restored PM resistance under ABA deficiency in ol‐2 plants. Overproduction of ET decreased ol‐2 ‐mediated resistance, which was associated with reduced callose deposition, and the suppression was more severe under salt stress (Kissoudis et al ., ).…”

“…The Ol‐4 NIL remained completely resistant under salt stress, and this was not influenced by deficiency in JA and ET pathways (Kissoudis et al ., ). Although this might suggest that the resistance conferred by Ol‐4 (a NBS‐LRR gene) is more stable than that conferred by other types of resistance genes like Ol‐1 or ol‐2 , this proposal is still speculative as there are no data available on the influence of other stress conditions and signaling pathways, such as the SA pathway, and other genes with similar resistance mechanisms.…”

“…habrochaites LYC4 were compromised. Further, cross‐talk among signaling pathways influenced the stability of the studied Ol‐ genes (Kissoudis et al ., , ). These results suggest that it is necessary to learn the identity of resistance genes and understand their function modes in relation to the target cultivation environment.…”

Cation Measurements and Gene Expression Analysis Suggest Tomato Leaf Marginal Necrosis is Caused by a Jasmonate Signal Induced by K⁺ Starvation in the Tip Region of Leaflets

“…Not only K + starvation, but also other stress signals are also known to induce leaf chlorosis. Since most abiotic stress signals are reported to be mediated by abscisic acid, ethylene, and jasmonates (Jibran et al, 2013;Zhang et al, 2011), the abscisic acid-and ethyleneresponsive genes, SlRD22 and Chi9, respectively (Kissoudis et al, 2017) were additionally examined to determine if these abiotic stress signals were activated (Fig. 4).…”