Abstract
Calcium is an important second messenger in plants that is released into the cytosol early after recognition of various environmental stimuli. Decoding of such calcium signals by calcium sensors is the key for the plant to react appropriately to each stimulus. Several members of Calmodulin-like proteins (CMLs) act as calcium sensors and some are known to mediate both abiotic and biotic stress responses. Here, we study the role of the Arabidopsis thaliana CML9 in different stress responses. CML9 was reported earlier as defense regulator against Pseudomonas syringae. In contrast to salicylic acid-mediated defense against biotrophic pathogens such as P. syringae, defenses against herbivores and necrotrophic fungi are mediated by jasmonates. We demonstrate that CML9 is induced upon wounding and feeding of the insect herbivore Spodoptera littoralis. However, neither different CML9 loss-of-function mutant lines nor overexpression lines were impaired upon insect feeding. No difference in herbivore-induced phytohormone elevation was detected in cml9 lines. The defense against the spider mite Tetranychus urticae was also unaffected. In addition, cml9 mutant lines showed a wild type-like reaction to the necrotrophic fungus Alternaria brassicicola. Thus, our data suggest that CML9 might be a regulator involved only in the defense against biotrophic pathogens, independent of jasmonates. In addition, our data challenge the involvement of CML9 in plant drought stress response. Taken together, we suggest that CML9 is a specialized rather than a general regulator of stress responses in Arabidopsis.
Highlights
IntroductionWhereas most of the organisms are able to escape unfavorable conditions, plants are sessile and need to cope up with these changes
The environment of organisms is continuously changing over their lifetime
We found that CML9 is significantly induced about 1.5-fold already after 30 min feeding of the chewing insect S. littoralis (Fig 1(A))
Summary
Whereas most of the organisms are able to escape unfavorable conditions, plants are sessile and need to cope up with these changes. They developed a plenty of strategies to overcome biotic as well as abiotic stresses throughout evolution [1,2,3]. Phytohormones play an essential role in these signaling pathways, such as abscisic acid (ABA) as key regulator of abiotic stress responses and salicylic acid (SA) and jasmonic acid (JA) as main mediators of biotic stress responses [3,4,5]. Plant-pathogen interactions are highly influenced by abiotic conditions and regulated by ABA as well [7]. The crosstalk between JA and SA has been largely investigated and several examples in herbivory and pathogen defense are known [3, 6, 8, 9]
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