Nitric oxide (NO) is a crucial signaling molecule that regulates a wide range of metabolic pathways in different strata of organisms. In plants, nitrate reductase (NR) is a key enzyme for NO biosynthesis. There are two NR-encoding genes in Arabidopsis, NIA1 and NIA2, which are precisely regulated and expressed in a tissue-specific manner. Here, we found that the natural antisense transcript as-NIA1, transcribed from the 3' UTR of NIA1, stabilizes NIA1 mRNA to maintain its circadian oscillation in plants grown under the light/dark cycle. Importantly, as-NIA1-dependent NIA1 mRNA stability is indispensable for NIA1-mediated NO biosynthesis in guard cells and natural stomatal closure. Moreover, we revealed that PTB3 regulates the stabilization of NIA1 mRNA by directly binding to UC-rich elements of as-NIA1. We further found that MTA deposits N6-methyladenosine (m6A) on as-NIA1, facilitating the as-NIA1-PTB3 interaction in vivo, in agreement with RNA structure prediction in that m6A-mediated structural alterations expose the UC-rich elements whereby enhancing the accessibility of PTB3. Our findings reveal a mechanism by which plants precisely manipulate NO biosynthesis to modulate light/dark-regulated stomatal movement, expanding the understanding of the coupling of RNA epigenetic modifications and structures shaping RNA‒protein interactions.
Keywords: N(6)-methyladenosine; NIA1; NO biosynthesis; natural antisense transcript; stomatal movement.
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