Cyclic Dipeptides from Bacillus vallismortis BS07 Require Key Components of Plant Immunity to Induce Disease Resistance in Arabidopsis against Pseudomonas Infection.

Cyclic dipeptides (CDPs) are one of the simplest compounds produced by living organisms. Plant-growth promoting rhizobacteria (PGPRs) also produce CDPs that can induce disease resistance. Bacillus vallismortis strain BS07 producing various CDPs has been evaluated as a potential biocontrol agent against multiple plant pathogens in chili pepper. However, plant signal pathway triggered by CDPs has not been fully elucidated yet. Here we introduce four CDPs, cyclo(Gly-L-Pro) previously identified from Aspergillus sp., and cyclo(L-Ala-L-Ile), cyclo(L-Ala-L-Leu), and cyclo(LLeu-L-Pro) identified from B. vallismortis BS07, which induce disease resistance in Arabidopsis against Pseudomonas syringae infection. The CDPs do not directly inhibit fungal and oomycete growth in vitro. These CDPs require PHYTOALEXIN DEFICIENT4, SALICYLIC ACID INDUCTION DEFICIENT2, and NONEXPRESSOR OF PATHOGENESIS-RELATED PROTEINS1 important for salicylic acid-dependent defense to induce resistance. On the other hand, regulators involved in jasmonate-dependent event, such as ETHYLENE RECEPTOR1, JASMONATE RESPONSE1, and JASMONATE INSENSITIVE1, are necessary to the CDP-induced resistance. Furthermore, treatment of these CDPs primes Arabidopsis plants to rapidly express PATHOGENESIS-RELATED PROTEIN4 at early infection phase. Taken together, we propose that these CDPs from PGPR strains accelerate activation of jasmonate-related signaling pathway during infection.

ALTERED MERISTEM PROGRAM1 has conflicting effects on the tolerance to heat shock and symptom development after Pseudomonas syringae infection.

An Arabidopsis thaliana ALTERED MERISTEM PROGRAM1 (AtAMP1), which encodes a putative glutamate carboxypeptidase, not only controls shoot apical meristem development, but also is involved in tolerance response to abiotic stresses. Here, we introduce a novel mutant; named amp1-32 that is a phenocopier to previously isolated different amp1 mutant alleles. Interestingly, tiny leaves were continuously developed at the bottom of pre-emerged leaves in the amp1-32. The amp1-32 mutant was less sensitive to heat shock treatment lasting for 3 h, whereas disease symptoms were severely developed in the mutant after Pseudomonas syringae infection. The mRNA levels of 171 genes were significantly altered in the mutant, as compared to wild-type plants. The transcription of genes involved in hormone signaling, post-embryonic development, and shoot development were up-regulated in the amp1-32 mutant, whereas expression of genes related to responsiveness to pathogens and (in)organic matters, were decreased in the mutant. Taken together, perturbation of CK- and ABA-related events by AMP1 mutation caused aberrant development phenotype and conflicting responses against abiotic and biotic stresses in Arabidopsis.

A Rice Gene Homologous to Arabidopsis AGD2-LIKE DEFENSE1 Participates in Disease Resistance Response against Infection with Magnaporthe oryzae.

ALD1 (ABERRANT GROWTH AND DEATH2 [AGD2]-LIKE DEFENSE1) is one of the key defense regulators in Arabidopsis thaliana and Nicotiana benthamiana. In these model plants, ALD1 is responsible for triggering basal defense response and systemic resistance against bacterial infection. As well ALD1 is involved in the production of pipecolic acid and an unidentified compound(s) for systemic resistance and priming syndrome, respectively. These previous studies proposed that ALD1 is a potential candidate for developing genetically modified (GM) plants that may be resistant to pathogen infection. Here we introduce a role of ALD1-LIKE gene of Oryza sativa, named as OsALD1, during plant immunity. OsALD1 mRNA was strongly transcribed in the infected leaves of rice plants by Magnaporthe oryzae, the rice blast fungus. OsALD1 proteins predominantly localized at the chloroplast in the plant cells. GM rice plants over-expressing OsALD1 were resistant to the fungal infection. The stable expression of OsALD1 also triggered strong mRNA expression of PATHOGENESIS-RELATED PROTEIN1 genes in the leaves of rice plants during infection. Taken together, we conclude that OsALD1 plays a role in disease resistance response of rice against the infection with rice blast fungus.