Abstract
Nucleotide-binding, leucine-rich repeat (NLR) genes play a pivotal role
in shaping plant effector-triggered immunity in response to pathogen
invasions. However, the mechanisms governing the expression and behavior
of NLRs, particularly in the context of head-to-head NLR gene pairs, in
the presence of pathogens, remain uncovered. In this study, we dissected
the Pik-H4 promoter (P Pik-H4) at the TATA
boxes and conducted an in-depth investigation into split promoter
activity using Agro-infiltration assays. The segments spanning 593-1232
bp and 2016-2492 bp (starting from -1 bp of
Pik1-H4) within P Pik-H4
emerged as core regions for expressing Pik1-H4
and Pik1-H4 respectively. Nevertheless, merging
these two core fragments failed to recover the promoter activity in both
directions. Employing Gus staining, promoter activity assays and
qRT-PCR, we unveiled the co-expression of Pik1-H4
and Pik2-H4 throughout the whole plant.
Additionally, in the presence of the rice blast fungus, their
co-amplification was observed in leaves and leaf sheaths. Strikingly,
Pik-H4 exhibited heightened expression within vascular bundles.
Moreover, perturbing the Pik1-H4 and
Pik2-H4 co-expression relationship via
overexpression in rice or Nicotiana did not disrupt the immune
response. Upon infection, the singleton Pik 1-H4
localized within vesicles, while Pik 2-H4 predominantly
occupied the nucleus within leaf sheath cells. Transcriptome analysis
highlighted Pik-H4-mediated resistance triggering a transcriptome
reprogramming between 12 and 24 hours post-inoculation. Notably,
overexpression of Pik1-H4 or
Pik2-H4 enriches various pathways compared to the
Pik-H4 Lijiangheituanxingu near-isogenic lines. In summary, these
findings unravel the intricate dynamics of co-expression and singular
functionality within NLR bidirectional gene pairs upon pathogen
invasion.