The rice peroxisomal receptor PEX5 negatively regulates resistance to rice blast fungus Magnaporthe oryzae.

The receptor protein PEX5, an important component of peroxisomes, regulates growth, development, and immunity in yeast and mammals. PEX5 also influences growth and development in plants, but whether it participates in plant immunity has remained unclear. Here, we report that knockdown of OsPEX5 enhances resistance to the rice blast fungus Magnaporthe oryzae. We demonstrate that OsPEX5 interacts with the E3 ubiquitin ligase APIP6, a positive regulator of plant immunity. APIP6 ubiquitinates OsPEX5 in vitro and promotes its degradation in vivo via the 26S proteasome pathway. In addition, OsPEX5 interacts with the aldehyde dehydrogenase OsALDH2B1, which functions in growth-defense trade-offs in rice. OsPEX5 stabilizes OsALDH2B1 to enhance its repression of the defense-related gene OsAOS2. Our study thus uncovers a previously unrecognized hierarchical regulatory mechanism in which an E3 ubiquitin ligase targets a peroxisome receptor protein that negatively regulates immunity in rice by stabilizing an aldehyde dehydrogenase that suppresses defense gene expression.

Reduction of cadmium accumulation in the grains of male sterile rice Chuang-5S carrying Pi48 or Pi49 through marker-assisted selection.

To reduce cadmium (Cd) accumulation in the grains of rice Chuang-5S (C5S), a gene OsHMA3 and a QTL qlGCd3 related to low-Cd accumulation were separately introgressed into the recipient parent C5S (male sterile line) by molecular marker-assisted breeding. The recurrent parent C5S was then replaced by NIL (near-isogenic line)-C5S with the blast resistance gene Pi48 or Pi49 to construct the BC2F1 generation. Finally, two groups of improved materials of C5S, which pyramided the gene/QTL associated with low-Cd accumulation and blast resistance gene, were developed. The Cd accumulation, agronomic traits, genetic background and blast resistance of these improved C5S materials were evaluated. The results showed that the average Cd content of improved C5S material carrying OsHMA3 and qlGCd3 was, respectively, reduced by 52.8% and 50.8% compared with that of C5S, indicating that the gene related to low-Cd accumulation was, successfully, transferred to C5S with stable expression. The main agronomic traits of the improved materials were consistent with those of C5S. Besides, the improved C5S lines showed stronger blast resistance than C5S and more than 88% similarity to the genetic background of C5S. These two groups of improved materials may be further utilized for the breeding of advanced male sterile lines or superior hybrid rice.