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The F-box protein MAX2 contributes to resistance to bacterial phytopathogens in Arabidopsis thaliana.

Piisilä M, Keceli MA, Brader G, Jakobson L, Jõesaar I, Sipari N, Kollist H, Palva ET, Kariola T - BMC Plant Biol. (2015)

Bottom Line: Interestingly, max2 mutant plants showed increased susceptibility to the bacterial necrotroph Pectobacterium carotovorum as well as to the hemi-biotroph Pseudomonas syringae but not to the fungal necrotroph Botrytis cinerea. max2 mutant phenotype was associated with constitutively increased stomatal conductance and decreased tolerance to apoplastic ROS but also with alterations in hormonal balance.We conclude that the increased susceptibility to P. syringae and P. carotovorum is due to increased stomatal conductance in max2 mutants promoting pathogen entry into the plant apoplast.Additional factors contributing to pathogen susceptibility in max2 plants include decreased tolerance to pathogen-triggered apoplastic ROS and alterations in hormonal signaling.

View Article: PubMed Central - PubMed

ABSTRACT

Background: The Arabidopsis thaliana F-box protein MORE AXILLARY GROWTH2 (MAX2) has previously been characterized for its role in plant development. MAX2 appears essential for the perception of the newly characterized phytohormone strigolactone, a negative regulator of polar auxin transport in Arabidopsis.

Results: A reverse genetic screen for F-box protein mutants altered in their stress responses identified MAX2 as a component of plant defense. Here we show that MAX2 contributes to plant resistance against pathogenic bacteria. Interestingly, max2 mutant plants showed increased susceptibility to the bacterial necrotroph Pectobacterium carotovorum as well as to the hemi-biotroph Pseudomonas syringae but not to the fungal necrotroph Botrytis cinerea. max2 mutant phenotype was associated with constitutively increased stomatal conductance and decreased tolerance to apoplastic ROS but also with alterations in hormonal balance.

Conclusions: Our results suggest that MAX2 previously characterized for its role in regulation of polar auxin transport in Arabidopsis, and thus plant development also significantly influences plant disease resistance. We conclude that the increased susceptibility to P. syringae and P. carotovorum is due to increased stomatal conductance in max2 mutants promoting pathogen entry into the plant apoplast. Additional factors contributing to pathogen susceptibility in max2 plants include decreased tolerance to pathogen-triggered apoplastic ROS and alterations in hormonal signaling.

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Expression of auxin marker genes inmax2lines are downregulated. Leaves from 4-week old soil grown wild-type Col-0 and max2 line plants were collected at indicated time points after P. syringae DC3000 infection and used to extract RNA to check the relative expression of auxin marker genes, AFB1(A) and TIR1(B). For this analysis, 3 plants/line and 3 leaves/plant were used. Results are based on a minimum of 3 independent experiments. Asterisks indicate significant differences, as determined by Student’s t-test (*P < 0.05; **P < 0.01; two-tailed t test).
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Fig8: Expression of auxin marker genes inmax2lines are downregulated. Leaves from 4-week old soil grown wild-type Col-0 and max2 line plants were collected at indicated time points after P. syringae DC3000 infection and used to extract RNA to check the relative expression of auxin marker genes, AFB1(A) and TIR1(B). For this analysis, 3 plants/line and 3 leaves/plant were used. Results are based on a minimum of 3 independent experiments. Asterisks indicate significant differences, as determined by Student’s t-test (*P < 0.05; **P < 0.01; two-tailed t test).

Mentions: MAX2 has been shown to negatively regulate polar auxin transport in Arabidopsis i.e. auxin transport is increased in max2 mutants [29]. Furthermore, the expression of SAUR-genes is enhanced in max2 plants indicating increased auxin response [58]. Auxin homeostasis has been shown to influence some plant-pathogen interactions [59] and interestingly, also max2 mutants were more sensitive to phytopathogens than wild-type plants. Thus, we wanted to explore whether auxin-related gene expression was also altered in max2 plants in response to P. syringae DC3000. Suprisingly, we noticed that the expression of the auxin receptor genes AUXIN SIGNALING F-BOX PROTEIN1 (AFB1) and TRANSPORT INHIBITOR RESPONSE1 (TIR1) was altered in max2 lines in comparison to wild-type plants. While P. syringae triggered AFB1 induction in wild-type plants, this was not observed in max2 plants (Figure 8A). Furthermore, TIR1 expression was decreased in max2 plants already before pathogen inoculation and remained in significantly lower level than in wild-type during the course of infection (Figure 8B). This could reflect the attempt of the plant to reduce the increased auxin response by downregulating the expression of the corresponding receptors.Figure 8


The F-box protein MAX2 contributes to resistance to bacterial phytopathogens in Arabidopsis thaliana.

Piisilä M, Keceli MA, Brader G, Jakobson L, Jõesaar I, Sipari N, Kollist H, Palva ET, Kariola T - BMC Plant Biol. (2015)

Expression of auxin marker genes inmax2lines are downregulated. Leaves from 4-week old soil grown wild-type Col-0 and max2 line plants were collected at indicated time points after P. syringae DC3000 infection and used to extract RNA to check the relative expression of auxin marker genes, AFB1(A) and TIR1(B). For this analysis, 3 plants/line and 3 leaves/plant were used. Results are based on a minimum of 3 independent experiments. Asterisks indicate significant differences, as determined by Student’s t-test (*P < 0.05; **P < 0.01; two-tailed t test).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
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getmorefigures.php?uid=PMC4340836&req=5

Fig8: Expression of auxin marker genes inmax2lines are downregulated. Leaves from 4-week old soil grown wild-type Col-0 and max2 line plants were collected at indicated time points after P. syringae DC3000 infection and used to extract RNA to check the relative expression of auxin marker genes, AFB1(A) and TIR1(B). For this analysis, 3 plants/line and 3 leaves/plant were used. Results are based on a minimum of 3 independent experiments. Asterisks indicate significant differences, as determined by Student’s t-test (*P < 0.05; **P < 0.01; two-tailed t test).
Mentions: MAX2 has been shown to negatively regulate polar auxin transport in Arabidopsis i.e. auxin transport is increased in max2 mutants [29]. Furthermore, the expression of SAUR-genes is enhanced in max2 plants indicating increased auxin response [58]. Auxin homeostasis has been shown to influence some plant-pathogen interactions [59] and interestingly, also max2 mutants were more sensitive to phytopathogens than wild-type plants. Thus, we wanted to explore whether auxin-related gene expression was also altered in max2 plants in response to P. syringae DC3000. Suprisingly, we noticed that the expression of the auxin receptor genes AUXIN SIGNALING F-BOX PROTEIN1 (AFB1) and TRANSPORT INHIBITOR RESPONSE1 (TIR1) was altered in max2 lines in comparison to wild-type plants. While P. syringae triggered AFB1 induction in wild-type plants, this was not observed in max2 plants (Figure 8A). Furthermore, TIR1 expression was decreased in max2 plants already before pathogen inoculation and remained in significantly lower level than in wild-type during the course of infection (Figure 8B). This could reflect the attempt of the plant to reduce the increased auxin response by downregulating the expression of the corresponding receptors.Figure 8

Bottom Line: Interestingly, max2 mutant plants showed increased susceptibility to the bacterial necrotroph Pectobacterium carotovorum as well as to the hemi-biotroph Pseudomonas syringae but not to the fungal necrotroph Botrytis cinerea. max2 mutant phenotype was associated with constitutively increased stomatal conductance and decreased tolerance to apoplastic ROS but also with alterations in hormonal balance.We conclude that the increased susceptibility to P. syringae and P. carotovorum is due to increased stomatal conductance in max2 mutants promoting pathogen entry into the plant apoplast.Additional factors contributing to pathogen susceptibility in max2 plants include decreased tolerance to pathogen-triggered apoplastic ROS and alterations in hormonal signaling.

View Article: PubMed Central - PubMed

ABSTRACT

Background: The Arabidopsis thaliana F-box protein MORE AXILLARY GROWTH2 (MAX2) has previously been characterized for its role in plant development. MAX2 appears essential for the perception of the newly characterized phytohormone strigolactone, a negative regulator of polar auxin transport in Arabidopsis.

Results: A reverse genetic screen for F-box protein mutants altered in their stress responses identified MAX2 as a component of plant defense. Here we show that MAX2 contributes to plant resistance against pathogenic bacteria. Interestingly, max2 mutant plants showed increased susceptibility to the bacterial necrotroph Pectobacterium carotovorum as well as to the hemi-biotroph Pseudomonas syringae but not to the fungal necrotroph Botrytis cinerea. max2 mutant phenotype was associated with constitutively increased stomatal conductance and decreased tolerance to apoplastic ROS but also with alterations in hormonal balance.

Conclusions: Our results suggest that MAX2 previously characterized for its role in regulation of polar auxin transport in Arabidopsis, and thus plant development also significantly influences plant disease resistance. We conclude that the increased susceptibility to P. syringae and P. carotovorum is due to increased stomatal conductance in max2 mutants promoting pathogen entry into the plant apoplast. Additional factors contributing to pathogen susceptibility in max2 plants include decreased tolerance to pathogen-triggered apoplastic ROS and alterations in hormonal signaling.

Show MeSH
Related in: MedlinePlus