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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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The expression of SA related marker genePR1is upregulated inmax2lines in response toP. syringae. Relative expression of PR1 after P. syringae infection. Four-week old soil-grown plants were sprayed with P.syringae and samples collected at indicated time points for extraction of RNA. Asterisks indicate significant differences, as determined by Student’s t-test (*P < 0.05; two-tailed t test). For each experiment, 3 plants/line and 3 leaves/plant were used.
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Fig10: The expression of SA related marker genePR1is upregulated inmax2lines in response toP. syringae. Relative expression of PR1 after P. syringae infection. Four-week old soil-grown plants were sprayed with P.syringae and samples collected at indicated time points for extraction of RNA. Asterisks indicate significant differences, as determined by Student’s t-test (*P < 0.05; two-tailed t test). For each experiment, 3 plants/line and 3 leaves/plant were used.

Mentions: SA is known to contribute to the resistance to P. carotovorum and P. syringae [2,3]. Considering the decreased pathogen resistance of max2 plants, in addition to the stomatal phenotype, the impact of possibly altered defense signaling could not be ruled out. To further explore the cause for the obvious decrease in plant resistance we characterized the expression of both SA- and JA-pathway marker genes in response to P. syringae infection. The expression of the marker gene for SA-dependent defense signaling, PR1 (PATHOGENESIS-RELATED GENE1) was significantly upregulated in wild-type plants 48 h after the spray inoculation. However, in max2 mutant plants PR1 was clearly induced already at 24 h and interestingly, at 48 h the expression of this gene was at least twice as high in max2 as that observed in wild-type plants (Figure 10). The expression of PR1 clearly indicates that the activation of SA-dependent defenses is enhanced in max2 plants. Intriguingly, despite this max2 plants are more susceptible to P. carotovorum and also P. syringae that should be contained by SA-mediated defense signaling.Figure 10


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)

The expression of SA related marker genePR1is upregulated inmax2lines in response toP. syringae. Relative expression of PR1 after P. syringae infection. Four-week old soil-grown plants were sprayed with P.syringae and samples collected at indicated time points for extraction of RNA. Asterisks indicate significant differences, as determined by Student’s t-test (*P < 0.05; two-tailed t test). For each experiment, 3 plants/line and 3 leaves/plant were used.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig10: The expression of SA related marker genePR1is upregulated inmax2lines in response toP. syringae. Relative expression of PR1 after P. syringae infection. Four-week old soil-grown plants were sprayed with P.syringae and samples collected at indicated time points for extraction of RNA. Asterisks indicate significant differences, as determined by Student’s t-test (*P < 0.05; two-tailed t test). For each experiment, 3 plants/line and 3 leaves/plant were used.
Mentions: SA is known to contribute to the resistance to P. carotovorum and P. syringae [2,3]. Considering the decreased pathogen resistance of max2 plants, in addition to the stomatal phenotype, the impact of possibly altered defense signaling could not be ruled out. To further explore the cause for the obvious decrease in plant resistance we characterized the expression of both SA- and JA-pathway marker genes in response to P. syringae infection. The expression of the marker gene for SA-dependent defense signaling, PR1 (PATHOGENESIS-RELATED GENE1) was significantly upregulated in wild-type plants 48 h after the spray inoculation. However, in max2 mutant plants PR1 was clearly induced already at 24 h and interestingly, at 48 h the expression of this gene was at least twice as high in max2 as that observed in wild-type plants (Figure 10). The expression of PR1 clearly indicates that the activation of SA-dependent defenses is enhanced in max2 plants. Intriguingly, despite this max2 plants are more susceptible to P. carotovorum and also P. syringae that should be contained by SA-mediated defense signaling.Figure 10

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