Heat stress transcription factor OsSPL7 plays a critical role in reactive oxygen species balance and stress responses in rice

The rice spotted leaf gene, OsSPL7, induces lesion mimic (LM) spots under heat stress. Herein, we provide several lines of evidence elucidating the importance of OsSPL7 in maintaining reactive oxygen species (ROS) balance via the regulation of downstream gene expression. osspl7 knockout (spl7ko) mutants showed LM and growth retardation. Transgenic rice lines strongly overexpressing OsSPL7 (SPL7OX-S) exhibited LM accompanied by accumulated H₂O₂, whereas moderate expressers of OsSPL7 (SPL7OX-M) did not, and neither of them exhibited severe growth defects. Transient expression of OsSPL7-GFP in rice protoplasts indicated that OsSPL7 localizes predominantly in the nucleus. Transcriptional activity assay suggested its function as a transcriptional activator in rice. Disease evaluation showed that both SPL7OX and spl7ko enhanced resistance to Magnaporthe oryzae and Xanthomonas oryzae pv. oryzae, the causal agents of blast and blight diseases in rice, respectively. Additionally, SPL7OX enhanced tolerance to cold stress, whereas spl7ko showed a phenotype opposite to the overexpression lines. RNA sequencing analyses identified four major groups of differentially expressed genes associated with LM, pathogen resistance, LM-pathogen resistance, and potential direct targets of OsSPL7. Collectively, our results suggest that OsSPL7 plays a critical role in plant growth and balancing ROS during biotic and abiotic stress.