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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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max2mutant lines have decreased resistance to spray inoculatedP. syringaeandP. carotovorum. Soil-grown four-week old plants were used to evaluate pathogen tolerance. In each experiment, three plants/line and three leaves/plant were used to check phenotype and to measure the bacterial concentration. All the experiments were repeated at least 4 times with similar results. The results are shown as means ± SE. (*P < 0.05; **P < 0.01; two-tailed t test). A) Phenotype of four week old wild-type Col-0 and max2 mutants after P.syringae infection with the concentration of 1x107 cfu/ml. Picture was taken 5 days post inoculation. Upper row shows non-treated plants and lower row P. syringae infected plants. B) Growth of P. syringae in planta was calculated at 0, 4, 8, 24, 48, 72 and 96 h after inoculation. C) Phenotype of max2 mutant lines after infection with P.carotovorum. Picture was taken 2 days post inoculation. D) Growth of P. carotovorum in planta 0, 6, 24 and 48 h after infection.
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Fig5: max2mutant lines have decreased resistance to spray inoculatedP. syringaeandP. carotovorum. Soil-grown four-week old plants were used to evaluate pathogen tolerance. In each experiment, three plants/line and three leaves/plant were used to check phenotype and to measure the bacterial concentration. All the experiments were repeated at least 4 times with similar results. The results are shown as means ± SE. (*P < 0.05; **P < 0.01; two-tailed t test). A) Phenotype of four week old wild-type Col-0 and max2 mutants after P.syringae infection with the concentration of 1x107 cfu/ml. Picture was taken 5 days post inoculation. Upper row shows non-treated plants and lower row P. syringae infected plants. B) Growth of P. syringae in planta was calculated at 0, 4, 8, 24, 48, 72 and 96 h after inoculation. C) Phenotype of max2 mutant lines after infection with P.carotovorum. Picture was taken 2 days post inoculation. D) Growth of P. carotovorum in planta 0, 6, 24 and 48 h after infection.

Mentions: The clearly altered stomatal phenotype implied that impaired expression of MAX2 gene could have an impact on pathogen tolerance in Arabidopsis. To elucidate this, we first investigated the susceptibility of max2 mutant lines to the virulent bacterial hemibiotroph P. syringae DC3000. To this aim we spray-inoculated max2 mutant lines and wild-type plants with the pathogen and followed the symptom development and bacterial growth in planta for five days. Interestingly, max2 mutant plants displayed clearly enhanced susceptibility to P. syringae observed both as heavy yellowing of the infected leaves as well as increased growth of the bacteria in the apoplast (Figure 5A and B). To further define the role of MAX2 in pathogen responses, we employed another type of pathogen, a bacterial necrotroph P. carotovorum, the causal agent of bacterial soft rot [52,53]. Interestingly, spray inoculation of the plants with P. carotovorum also resulted in enhanced disease development in the max2 mutant lines seen as more extensive tissue maceration when compared to wild-type plants (Figure 5C and D) indicating that the defense-associated role of MAX2 is not dependent on the pathogen lifestyle.Figure 5


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)

max2mutant lines have decreased resistance to spray inoculatedP. syringaeandP. carotovorum. Soil-grown four-week old plants were used to evaluate pathogen tolerance. In each experiment, three plants/line and three leaves/plant were used to check phenotype and to measure the bacterial concentration. All the experiments were repeated at least 4 times with similar results. The results are shown as means ± SE. (*P < 0.05; **P < 0.01; two-tailed t test). A) Phenotype of four week old wild-type Col-0 and max2 mutants after P.syringae infection with the concentration of 1x107 cfu/ml. Picture was taken 5 days post inoculation. Upper row shows non-treated plants and lower row P. syringae infected plants. B) Growth of P. syringae in planta was calculated at 0, 4, 8, 24, 48, 72 and 96 h after inoculation. C) Phenotype of max2 mutant lines after infection with P.carotovorum. Picture was taken 2 days post inoculation. D) Growth of P. carotovorum in planta 0, 6, 24 and 48 h after infection.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig5: max2mutant lines have decreased resistance to spray inoculatedP. syringaeandP. carotovorum. Soil-grown four-week old plants were used to evaluate pathogen tolerance. In each experiment, three plants/line and three leaves/plant were used to check phenotype and to measure the bacterial concentration. All the experiments were repeated at least 4 times with similar results. The results are shown as means ± SE. (*P < 0.05; **P < 0.01; two-tailed t test). A) Phenotype of four week old wild-type Col-0 and max2 mutants after P.syringae infection with the concentration of 1x107 cfu/ml. Picture was taken 5 days post inoculation. Upper row shows non-treated plants and lower row P. syringae infected plants. B) Growth of P. syringae in planta was calculated at 0, 4, 8, 24, 48, 72 and 96 h after inoculation. C) Phenotype of max2 mutant lines after infection with P.carotovorum. Picture was taken 2 days post inoculation. D) Growth of P. carotovorum in planta 0, 6, 24 and 48 h after infection.
Mentions: The clearly altered stomatal phenotype implied that impaired expression of MAX2 gene could have an impact on pathogen tolerance in Arabidopsis. To elucidate this, we first investigated the susceptibility of max2 mutant lines to the virulent bacterial hemibiotroph P. syringae DC3000. To this aim we spray-inoculated max2 mutant lines and wild-type plants with the pathogen and followed the symptom development and bacterial growth in planta for five days. Interestingly, max2 mutant plants displayed clearly enhanced susceptibility to P. syringae observed both as heavy yellowing of the infected leaves as well as increased growth of the bacteria in the apoplast (Figure 5A and B). To further define the role of MAX2 in pathogen responses, we employed another type of pathogen, a bacterial necrotroph P. carotovorum, the causal agent of bacterial soft rot [52,53]. Interestingly, spray inoculation of the plants with P. carotovorum also resulted in enhanced disease development in the max2 mutant lines seen as more extensive tissue maceration when compared to wild-type plants (Figure 5C and D) indicating that the defense-associated role of MAX2 is not dependent on the pathogen lifestyle.Figure 5

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