MoHTR1, a Nuclear Effector of the Rice Blast Fungus, Regulates Alternative Splicing of Rice Immunity Genes.

Plant pathogens deploy nuclear effectors to manipulate the host immune response and reprogram cellular processes. Alternative splicing, a key RNA processing mechanism, plays a pivotal role in determining the fate of immune response-associated genes. Some nuclear effectors have been studied for their roles in the transcription or post-transcriptional regulation of host genes. However, the understanding of how a single nuclear effector engages in multiple regulatory processes within the host nucleus remains limited. Previously, we demonstrated that MoHTR1, a nuclear effector of the rice blast fungus, binds to effector binding elements in the promoters of target genes and modulates host immunity. To further explore the multifunctionality of MoHTR1, we identified host proteins interacting with MoHTR1. MoHTR1 interacts with the splicing factor OsSR45 in rice nuclear speckles and promotes degradation of OsSR45. MoHTR1 is involved in alternative splicing of mRNAs associated with immune and stress responses. The changes in alternative splicing patterns of these mRNAs are identical in both Magnaporthe oryzae-infected rice and MoHTR1-overexpressing transgenic lines, underscoring the consistent regulatory effect of MoHTR1. Our findings highlight dual roles of MoHTR1 in regulating both transcription and post-transcriptional processes, and providing novel insights into how nuclear effectors modulate host immunity through intricate molecular mechanisms.