Amandine Delteil, Enrico Gobbato, Bastien Cayrol, Joan Estevan, Corinne Michel-Romiti, Anne Dievart, Thomas Kroj and J.-B. Morel

BMC Plant Biology BMC series – open, inclusive and trusted 2016 16:17, DOI: 10.1186/s12870-016-0711-x

Abstract

Background

Receptor-like kinases are well-known to play key roles in disease resistance. Among them, the Wall-associated kinases (WAKs) have been shown to be positive regulators of fungal disease resistance in several plant species. WAK genes are often transcriptionally regulated during infection but the pathways involved in this regulation are not known. In rice, the OsWAK gene family is significantly amplified compared to Arabidopsis. The possibility that several WAKs participate in different ways to basal defense has not been addressed. Moreover, the direct requirement of rice OSWAK genes in regulating defense has not been explored.

Results

Here we show using rice (Oryza sativa) loss-of-function mutants of four selected OsWAK genes, that individual OsWAKs are required for quantitative resistance to the rice blast fungus, Magnaporthe oryzae. While OsWAK14, OsWAK91 and OsWAK92 positively regulate quantitative resistance, OsWAK112d is a negative regulator of blast resistance. In addition, we show that the very early transcriptional regulation of the rice OsWAK genes is triggered by chitin and is partially under the control of the chitin receptor CEBiP. Finally, we show that OsWAK91 is required for H₂O₂ production and sufficient to enhance defense gene expression during infection.

Conclusions

We conclude that the rice OsWAK genes studied are part of basal defense response, potentially mediated by chitin from fungal cell walls. This work also shows that some OsWAKs, like OsWAK112d, may act as negative regulators of disease resistance.

See http://bmcplantbiol.biomedcentral.com/articles/10.1186/s12870-016-0711-x

Fig. 3

OsWAK91 and OsWAK112d over-expresser lines are affected for M. oryzae resistance. Expression of OsWAK91 and OsWAK112d was measured by quantitative RT-PCR in non-infected lines over-expressing (OE) OsWAK91 (a) or OsWAK112d (b) genes and the corresponding null-segregant lines (NS). Gene expression, calculated from three biological replicates, was normalized using Actin. The fold change between NS and OE is also indicated (a and b). Plants were inoculated with the virulent isolate GY11 of M. oryzae. The total number of lesions was counted as in Fig. 2 in the lines OE-OsWAK91 (c) or OE-OsWAK112d (d). For each mutant line, the average number of lesions over more than 7 plants was calculated for the corresponding over-expresser and null-segregant line. This value was used to calculate the percentage of lesions per individual mutant plant as compared to the mean of the null-segregant plants. The mean and standard deviation was then calculated. This experiment was repeated three times and one representative experiment is shown. A t-test was done to evaluate the significance of the observed differences (*: p <0.05; **: p <0.001). Pictures of typical symptoms on over-expresser and null-segregant lines were taken 5 days post inoculation (e and f). Several other over-expresser lines were also produced and analyzed (Additional file 4)