Joy Michal Johnson

Piriformospora indica confers drought tolerance in Chinese cabbage leaves by stimulating antioxidant enzymes, the expression of drought-related genes and the plastid-localized CAS protein

Piriformospora indica, a root-colonizing endophytic fungus of Sebacinales, promotes plant growth and confers resistance against biotic and abiotic stress. The fungus strongly colonizes the roots of Chinese cabbage, promotes root and shoot growth, and promotes lateral root formation. When colonized plants were exposed to polyethylene glycol to mimic drought stress, the activities of peroxidases, catalases and superoxide dismutases in the leaves were upregulated within 24h. The fungus retarded the drought-induced decline in the photosynthetic efficiency and the degradation of chlorophylls and thylakoid proteins. The expression levels of the drought-related genes DREB2A, CBL1, ANAC072 and RD29A were upregulated in the drought-stressed leaves of colonized plants. Furthermore, the CAS mRNA level for the thylakoid membrane associated Ca(2+)-sensing regulator and the amount of the CAS protein increased. We conclude that antioxidant enzyme activities, drought-related genes and CAS are three crucial targets of P. indica in Chinese cabbage leaves during the establishment of drought tolerance. P. indica-colonized Chinese cabbage provides a good model system to study root-to-shoot communication.

Piriformospora indica: The versatile and multifunctional root endophytic fungus for enhanced yield and tolerance to biotic and abiotic stress in crop plants

Owing to its exceptional ability to efficiently promote plant growth, protection and stress tolerance, a mycorrhiza like endophytic Agaricomycetes fungus Piriformospora indica has received a great attention over the last few decades. P. indica is an axenically cultiviable fungus which exhibits its versatility for colonizing/hosting a broad range of plant species through directly manipulating plant hormone-signaling pathway during the course of mutualism. P. indica-root colonization leads to a better plant performance in all respect, including enhanced root proliferation by indole-3-acetic acid production which in turn results into better nutrient-acquisition and subsequently to improved crop growth and productivity. Additionally, P. indica can induce both local and systemic resistance to fungal and viral plant diseases through signal transduction. P. indica-mediated stimulation in antioxidant defense system components and expressing stress-related genes can confer crop/plant stress tolerance. Therefore, P. indica can biotize micropropagated plantlets and also help these plants to overcome transplantation shock. Nevertheless, it can also be involved in a more complex symbiotic relationship, such as tripartite symbiosis and can enhance population dynamic of plant growth promoting rhizobacteria. In brief, P. indica can be utilized as a plant promoter, bio-fertilizer, bioprotector, bioregulator, and biotization agent. The outcome of the recent literature appraised herein will help us to understand the physiological and molecular bases of mechanisms underlying P. indica-crop plant mutual relationship. Together, the discussion will be functional to comprehend the usefulness of crop plant-P. indica association in both achieving new insights into crop protection/improvement as well as in sustainable agriculture production.

Growth Promotion of Chinese Cabbage and Arabidopsis by Piriformospora indica Is Not Stimulated by Mycelium-Synthesized Auxin

Piriformospora indica, an endophytic fungus of the order Sebacinales, interacts with the roots of a large variety of plant species. We compared the interaction of this fungus with Chinese cabbage (Brassica campestris subsp. chinensis) and Arabidopsis seedlings. The development of shoots and roots of Chinese cabbage seedlings was strongly promoted by P. indica and the fresh weight of the seedlings increased approximately twofold. The strong stimulation of root hair development resulted in a bushy root phenotype. The auxin level in the infected Chinese cabbage roots was twofold higher compared with the uncolonized controls. Three classes of auxin-related genes, which were upregulated by P. indica in Chinese cabbage roots, were isolated from a double-subtractive expressed sequence tag library: genes for proteins related to cell wall acidification, intercellular auxin transport carrier proteins such as AUX1, and auxin signal proteins. Overexpression of B. campestris BcAUX1 in Arabidopsis strongly promoted growth and biomass production of Arabidopsis seedlings and plants; the roots were highly branched but not bushy when compared with colonized Chinese cabbage roots. This suggests that BcAUX1 is a target of P. indica in Chinese cabbage. P. indica also promoted growth of Arabidopsis seedlings but the auxin levels were not higher and auxin genes were not upregulated, implying that auxin signaling is a more important target of P. indica in Chinese cabbage than in Arabidopsis. The fungus also stimulated growth of Arabidopsis aux1 and aux1/axr4 and rhd6 seedlings. Furthermore, a component in an exudate fraction from P. indica but not auxin stimulated growth of Chinese cabbage and Arabidopsis seedlings. We propose that activation of auxin biosynthesis and signaling in the roots might be the cause for the P. indica-mediated growth phenotype in Chinese cabbage.

Indole-3-Acetaldoxime-Derived Compounds Restrict Root Colonization in the Beneficial Interaction Between Arabidopsis Roots and the Endophyte Piriformospora indica

The growth-promoting and root-colonizing endophyte Piriformospora indica induces camalexin and the expression of CYP79B2, CYP79B3, CYP71A13, PAD3, and WRKY33 required for the synthesis of indole-3-acetaldoxime (IAOx)-derived compounds in the roots of Arabidopsis seedlings. Upregulation of the mRNA levels by P. indica requires cytoplasmic calcium elevation and mitogen-activated protein kinase 3 but not root-hair-deficient 2, radical oxygen production, or the 3-phosphoinositide-dependent kinase 1/oxidative signal-inducible 1 pathway. Because P. indica-mediated growth promotion is impaired in cyp79B2 cyp79B3 seedlings, while pad3 seedlings-which do not accumulate camalexin-still respond to the fungus, IAOx-derived compounds other than camalexin (e.g., indole glucosinolates) are required during early phases of the beneficial interaction. The roots of cyp79B2 cyp79B3 seedlings are more colonized than wild-type roots, and upregulation of the defense genes pathogenesis-related (PR)-1, PR-3, PDF1.2, phenylalanine ammonia lyase, and germin indicates that the mutant responds to the lack of IAOx-derived compounds by activating other defense processes. After 6 weeks on soil, defense genes are no longer upregulated in wild-type, cyp79B2 cyp79B3, and pad3 roots. This results in uncontrolled fungal growth in the mutant roots and reduced performance of the mutants. We propose that a long-term harmony between the two symbionts requires restriction of root colonization by IAOx-derived compounds.

Piriformospora indica promotes growth of chinese cabbage by manipulating auxin homeostasis - Role of auxin in symbiosis

We study the symbiotic interaction of an endophytic fungus Piriformospora indica with different plant species. The ubiquitous fungus promotes growth of all plant species which have been tested so far, including the model plant Arabidopsis thaliana and the agriculturally important crop Chinese cabbage. Growth promotion of these two plant species by P. indica involves auxin; however, the role of this phytohormone in the two symbioses is quite different. The comparative analysis of these two symbioses allows interesting conclusions of how P. indica controls growth programs on the basis of different genetic backgrounds of individual plant species.

Standardized conditions to study beneficial and nonbeneficial traits in the Piriformospora indica/Arabidopsis thaliana interaction

The endophytic root colonizing fungus, Piriformospora indica, interacts with the model plant Arabidopsis thaliana and promotes growth, biomass, and seed production and also confers resistance against biotic and abiotic stress. To identify genes, proteins, and biomolecules from the plant which are required for the mutualistic interaction between the two symbionts, beneficial and nonbeneficial traits must be measured and accurately quantified during the whole life of the plant. The fungus also enhances host resistance by the activation of induced systemic resistance against Alternaria brassicae and also protects the plant by direct antagonism to the invading pathogens. We have established standardized cocultivation conditions which allow to monitor these traits and which are described in this chapter.

A poly(A) ribonuclease controls the cellotriose-based interaction between Piriformospora indica and its host Arabidopsis

The elicitor-active cell wall moiety of the endophytic fungus Piriformospora indica, cellotriose, modulates the plant-fungus symbiosis by activating a poly(A) ribonuclease in Arabidopsis. Piriformospora indica, an endophytic root-colonizing fungus, efficiently promotes plant growth and induces resistance to abiotic stress and biotic diseases. P. indica fungal cell wall extract induces cytoplasmic calcium elevation in host plant roots. Here, we show that cellotriose (CT) is an elicitor-active cell wall moiety released by P. indica into the medium. CT induces a mild defense-like response, including the production of reactive oxygen species, changes in membrane potential, and the expression of genes involved in growth regulation and root development. CT-based cytoplasmic calcium elevation in Arabidopsis (Arabidopsis thaliana) roots does not require the BAK1 coreceptor or the putative Ca2+ channels TPC1, GLR3.3, GLR2.4, and GLR2.5 and operates synergistically with the elicitor chitin. We identified an ethyl methanesulfonate-induced mutant (cytoplasmic calcium elevation mutant) impaired in the response to CT and various other cellooligomers (n = 2–7), but not to chitooligomers (n = 4–8), in roots. The mutant contains a single nucleotide exchange in the gene encoding a poly(A) ribonuclease (AtPARN; At1g55870) that degrades the poly(A) tails of specific mRNAs. The wild-type PARN cDNA, expressed under the control of a 35S promoter, complements the mutant phenotype. Our identification of cellotriose as a novel chemical mediator casts light on the complex P. indica-plant mutualistic relationship.

Balancing defense and growth—Analyses of the beneficial symbiosis between Piriformospora indica and Arabidopsis thaliana

The mutualistic interaction between the endophytic and root-colonizing fungus Piriformospora indica and Arabidopsis thaliana is a nice model system to study beneficial and non-benefical traits in a symbiosis. Colonized Arabidopsis plants are taller, produce more seeds and are more resistant against biotic and abiotic stress. Based on genetic, molecular and cellular analyses, Arabidopsis mutants were identified which are impaired in their beneficial response to the fungus. Several mutants are smaller rather than bigger in the presence of the fungus and are defective in defense responses. This includes mutants with defects in defense-signaling components, defense proteins and enzymes, and defense metabolites. The mutants cannot control root colonization and are often over-colonized by P. indica. As a consequence, the benefits for the plants are lost and they try to restrict root colonization by activating unspecific defense responses against P. indica. These observations raise the question as to how the plants balance defense gene activation or development and what signaling molecules are involved. P. indica promotes the synthesis of phosphatidic acid (PA), which binds to the 3-PHOSPHOINOSITIDE-DEPENDENT-KINASE1 (PDK1). This activates a kinase pathway which might be crucial for balancing defense and growth responses. The review describes plant defense compounds which are necessary for the mutualistic interaction between the two symbionts. Furthermore, it is proposed that the PA/PDK1 pathway may be crucial for balancing defense responses and growth stimulation during the interaction with P. indica.