Building a mutant resource for the study of disease resistance in rice reveals the pivotal role of several genes involved in defence

Abstract

In Arabidopsis, gene expression studies and analysis of knock-out (KO) mutants have been instrumental in building an integrated view of disease resistance pathways. Such an integrated view is missing in rice where shared tools, including genes and mutants, must be assembled. This work provides a tool kit consisting of informative genes for the molecular characterization of the interaction of rice with the major fungal pathogen Magnaporthe oryzae. It also provides for a set of eight KO mutants, all in the same genotypic background, in genes involved in key steps of the rice disease resistance pathway. This study demonstrates the involvement of three genes, OsWRKY28, rTGA2.1 and NH1, in the establishment of full basal resistance to rice blast. The transcription factor OsWRKY28 acts as a negative regulator of basal resistance, like the orthologous barley gene. Finally, the up-regulation of the negative regulator OsWRKY28 and the down-regulation of PR gene expression early during M. oryzae infection suggest that the fungus possesses infection mechanisms that enable it to block host defences.

OsMADS26 negatively regulates resistance to pathogens and drought tolerance in rice.

“…GSE7256), we further investigated its expression time course after inoculation with virulent and avirulent isolates (FR13 and CL3.6.7, respectively;Delteil et al, 2012) of M. oryzae (Fig. 3).…”

“…First, plantlets of the different OsMADS26 lines were inoculated with the moderately virulent fungal isolate GUY11 of M. oryzae (Delteil et al, 2012). This isolate triggers lesions in the leaf blade of cv Nipponbare consisting of an average of 50% grayish lesions surrounded by brown margins that are characteristic of successful invasion of the fungus (disease).…”

“…In this experiment, the number of susceptible lesions was significantly higher in OX2 line and slightly lower in DR3-1 line than in the control (OX0), confirming the opposite phenotypes observed for overexpressing and down-regulated OsMADS26 lines. The expression of a set of selected major defenserelated genes, PEROXIDASE22.3 (POX22.3; Vergne et al, 2007), CHITINASE7 (CHI7; Kaku et al, 2006), Chern et al, 2005), (FLAGELLIN SENSING2), OsWRKY28, and PROBENAZOLE-INDUCIBLE1 (PBZ1; Delteil et al, 2012), was examined in OX2 lines 2 dpi with M. oryzae GY11 isolate or mock treatment (Fig. 6).…”

“…For gene expression studies (Fig. 3), we used the fully virulent FR13 isolate and the avirulent isolate CL3.6.7 (Delteil et al, 2012). In laboratory, inoculations were performed on four-to five-leaf stage plantlets as described in Berruyer et al, 2003; rice japonica 'Maratelli' was used as a susceptible control in the experiments in addition to the studied transgenic lines.…”

“…For gene expression studies (Fig. 3), we used the fully virulent FR13 isolate and the avirulent isolate CL3.6.7 (Delteil et al, 2012). Leaves were collected before and after inoculation in liquid nitrogen and used for RNA extraction and qRT-PCR analysis to measure the expression level of different defense genes using specific primers (Supplemental Table S2).…”