Abstract
The rice pathogenesis-related protein OsPR10a was scarcely expressed in OsCDPK1-silenced (Ri-1) rice, which was highly sensitive to pathogen infection. After inoculating the leaves with bacterial blight (Xanthomonas oryzae pv. oryzae; Xoo), we found that the expression of OsPR10a was up- and down-regulated in OEtr-1 (overexpression of the constitutively active truncated form of OsCDPK1) and Ri-1 rice plants, respectively. OsPR10a and OsCDPK1 showed corresponding expression patterns and were up-regulated in response to the jasmonic acid, salicylic acid and Xoo treatments, and OsPR1 and OsPR4 were significantly up-regulated in OEtr-1. These results suggest that OsCDPK1 may be an upstream regulator involved in rice innate immunity and conferred broad-spectrum of disease resistance. Following the Xoo inoculation, the OEtr-1 and Ri-1 seedlings showed enhanced and reduced disease resistance, respectively. The dihybrid rice Ri-1/OsPR10a-Ox not only bypassed the effect of OsCDPK1 silencing on the susceptibility to Xoo but also showed enhanced disease resistance and, consistent with Ri-1 phenotypes, increased plant height and grain size. Our results reveal that OsCDPK1 plays novel key roles in the cross-talk and mediation of the balance between stress response and development and provides a clue for improving grain yield and disease resistance simultaneously in rice.
Highlights
In prokaryotic and eukaryotic cells, calcium ions (Ca2+) are intracellular second messengers that enable the sensing of a variety of environmental and developmental stimuli through temporal and spatial fluctuations or elevations in cytosolic Ca2+ concentrations[1,2]
We show that the protein kinase OsCDPK1 functions as a positive effector of OsPR10a in rice
OsPR10a (PBZ1) is induced by exogenous salicylic acid (SA), jasmonic acid (JA), Xoo, and the blast fungus Magnaporthe grisea[28,38,39,40], suggesting that OsPR10a might confer broad-spectrum resistance to pathogens. These findings are consistent with the present results, and we showed that both OsCDPK1 and OsPR10a were synergistically up-regulated by the treatment with SA (100 μM) and/or JA (100 μM) or infection by the biotrophic pathogen Xoo (Fig. 3; Supplementary Fig. S4)
Summary
In prokaryotic and eukaryotic cells, calcium ions (Ca2+) are intracellular second messengers that enable the sensing of a variety of environmental and developmental stimuli through temporal and spatial fluctuations or elevations in cytosolic Ca2+ concentrations[1,2]. In Arabidopsis, the overexpression of the lipid-bodies and peroxisomal localized protein AtCPK1 results in the accumulation of salicylic acid (SA), which subsequently confers resistance to the pathogen Fusarium oxysporum, suggesting that lipid bodies have a function in plant innate immunity[19]. The overexpression of OsCPK12 enhances tolerance to salt stress by reducing reactive oxygen species production but increases sensitivity to a blast fungus challenge[23]. Rice OsCPK18 was identified as an upstream kinase responsible for the phosphorylation and activation of OsMPK5, leading to the inhibition of the expression of defense-related genes (PR5, PR10, and chitinase) and negative regulation of blast fungus (Magnaporthe oryzae) resistance[24]. Overexpression of OsCPK4 positively regulates salt and drought stress tolerance by reducing membrane lipid peroxidation[25] and enhances resistance to M. oryzae infection by preventing fungal penetration[26]. The dihybrid rice Ri-1/OsPR10a-Ox, which is derived from a cross between an OsPR10a overexpression line (OsPR10a-Ox) and an RNA interference knockdown of OsCDPK1 line (OsCDPK1-Ri; Ri-1), has a greater plant height, a larger seed size, and enhanced resistance to Xoo infection
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