Jung GY, Park JY, Choi HJ, Yoo SJ, Park JK, Jung HW.

Plant Pathol J. 2016 Aug;32(4):357-62. doi: 10.5423/PPJ.NT.10.2015.0213. Epub 2016 Aug 1.

Abstract

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.

See: http://dx.doi.org/10.5423/PPJ.NT.10.2015.0213

Figure 1: An OsALD1 gene, whose products accumulated at chloroplast, was strongly expressed in the infected leaves of rice plants with rice blast fungus. (A) Symptom development of rice blast disease in Oryza sativa cv. Dongjin infected by a Magnaporthe oryzae KJ-105a isolate. (B) Fungal growth was verified by quantifying expression of M. oryzae β-Tubulin2 (MoTUB). The relative expression level was calculated by a 2^−ΔΔCT method (Livak and Schmittgen, 2001). A rice ubiquitin gene was used as an internal reference gene. (C, D) Infection with the rice blast fungus triggered expression of O. sativa PATHOGENESIS-RELATED PROTEIN1b (OsPR1b) (C) and OsALD1 (D) genes in the infected leaf tissues. Relative expression ratios were computed by a standard curve-based method (Pfaffl, 2001). mRNA levels of each sample were normalized by that of cv. Dongjin plants before mock-inoculation. Data represent the average with standard deviation (n = 3). Either fungal spore suspension (gray bars) (5 × 10⁵ conidia/ml) or water (white bars) was inoculated with a paintbrush on the leaves (A–D). These experiments were repeated twice with the same results. (E) OsALD1 proteins localized at chloroplast in the leaves of Nicotiana benthamiana. OsALD1:GFP construct, whose expression was conditionally controlled by dexamethasone (DEX)-inducible promoter, was introduced in the leaves of N. benthamiana in accordance with an Agrobacterium-mediated transient expression protocol. Green fluorescence protein (GFP) was visualized 1 day after DEX (30 μM) treatment under a confocal microscopy (× 100). DAI, days after inoculation.