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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 oxidative stress marker genes inmax2lines is upregulated. Mature leaves of 4-week old soil grown wild-type Col-0 and max2 plants were collected at indicated time points after P. syringae DC3000 infection and RNA was extracted to check the relative expression of oxidative stress marker gene GRX480 after 350 ppb for 6 h ozone exposure (A) and after pathogen infection (B). Another oxidative stress marker gene GST1(C) and auxin-responsive gene HAT2(D) also checked after pathogen infection. For this analysis, 3 plants/line and 3 leaves/plant were used in each time point of infection and ozonation. Each expression analysis is 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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Fig7: The expression of oxidative stress marker genes inmax2lines is upregulated. Mature leaves of 4-week old soil grown wild-type Col-0 and max2 plants were collected at indicated time points after P. syringae DC3000 infection and RNA was extracted to check the relative expression of oxidative stress marker gene GRX480 after 350 ppb for 6 h ozone exposure (A) and after pathogen infection (B). Another oxidative stress marker gene GST1(C) and auxin-responsive gene HAT2(D) also checked after pathogen infection. For this analysis, 3 plants/line and 3 leaves/plant were used in each time point of infection and ozonation. Each expression analysis is 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: The enhanced sensitivity of max2 mutants to apoplastic ROS (Figure 2) suggested that MAX2 could be involved in responses to oxidative stress. Since both ozone and pathogen infection trigger apoplastic ROS formation, we wanted to study the induction of ROS-responsive genes in max2 and wild-type plants in response to these stresses. For this, we first characterized the expression of GRX480 encoding a glutaredoxin family protein, that is an early ROS responsive gene and is also triggered by ozone [55,56]. Ozone triggered overall higher expression of GRX480 than P. syringae but in both cases the induction of this gene was clearly higher in max2 than in wild-type plants (Figure 7A and B). We also characterized the expression of oxidative stress marker gene GST1 (ARABIDOPSIS GLUTATHIONE S TRANSFERASE1) [57] in response to P. syringae. Similarly to GRX480 the accumulation of GST1 transcripts was also enhanced in max2 plants when compared to wild-type plants but to higher level (Figure 7C). These observations suggest that max2 plants might be more sensitive to ROS and that MAX2 is involved in oxidative stress responses.Figure 7


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 oxidative stress marker genes inmax2lines is upregulated. Mature leaves of 4-week old soil grown wild-type Col-0 and max2 plants were collected at indicated time points after P. syringae DC3000 infection and RNA was extracted to check the relative expression of oxidative stress marker gene GRX480 after 350 ppb for 6 h ozone exposure (A) and after pathogen infection (B). Another oxidative stress marker gene GST1(C) and auxin-responsive gene HAT2(D) also checked after pathogen infection. For this analysis, 3 plants/line and 3 leaves/plant were used in each time point of infection and ozonation. Each expression analysis is 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
Show All Figures
getmorefigures.php?uid=PMC4340836&req=5

Fig7: The expression of oxidative stress marker genes inmax2lines is upregulated. Mature leaves of 4-week old soil grown wild-type Col-0 and max2 plants were collected at indicated time points after P. syringae DC3000 infection and RNA was extracted to check the relative expression of oxidative stress marker gene GRX480 after 350 ppb for 6 h ozone exposure (A) and after pathogen infection (B). Another oxidative stress marker gene GST1(C) and auxin-responsive gene HAT2(D) also checked after pathogen infection. For this analysis, 3 plants/line and 3 leaves/plant were used in each time point of infection and ozonation. Each expression analysis is 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: The enhanced sensitivity of max2 mutants to apoplastic ROS (Figure 2) suggested that MAX2 could be involved in responses to oxidative stress. Since both ozone and pathogen infection trigger apoplastic ROS formation, we wanted to study the induction of ROS-responsive genes in max2 and wild-type plants in response to these stresses. For this, we first characterized the expression of GRX480 encoding a glutaredoxin family protein, that is an early ROS responsive gene and is also triggered by ozone [55,56]. Ozone triggered overall higher expression of GRX480 than P. syringae but in both cases the induction of this gene was clearly higher in max2 than in wild-type plants (Figure 7A and B). We also characterized the expression of oxidative stress marker gene GST1 (ARABIDOPSIS GLUTATHIONE S TRANSFERASE1) [57] in response to P. syringae. Similarly to GRX480 the accumulation of GST1 transcripts was also enhanced in max2 plants when compared to wild-type plants but to higher level (Figure 7C). These observations suggest that max2 plants might be more sensitive to ROS and that MAX2 is involved in oxidative stress responses.Figure 7

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