SlYTH3 regulates tomato leaf senescence via recognition of N6-methyladenosine-modified SlHDZIV2 transcripts

N 6-methyladenosine (m6A) is the most abundant internal modification in eukaryotic mRNA, with essential roles in plant development and stress adaptation. However, its regulatory function in leaf senescence remains poorly defined. Here, we demonstrate that tomato (Solanum lycopersicum) leaf aging is accompanied by dynamic changes in m6A levels and that YT521-B homology (YTH) domain protein 3 (SlYTH3) acts as an m6A reader to preserve leaf longevity by recognizing m6A-modified transcripts of HOMEODOMAIN-LEUCINE ZIPPER IV 2 (SlHDZIV2). Loss of SlYTH3 accelerates dark-induced leaf senescence, leading to chloroplast disruption, photosynthetic impairment, and premature activation of senescence-associated genes. Mechanistically, SlYTH3 binds to the canonical m6A motif (RRACH) within SlHDZIV2 mRNA, enhancing both its transcript stability and translation efficiency. Genetic analyses confirmed that SlHDZIV2 functions downstream of SlYTH3. Furthermore, SlHDZIV2 directly activates transcription of autophagy-related 5 (SlATG5), thereby sustaining autophagic activity during senescence. Disruption of this regulatory cascade in slhdziv2 or slatg5 mutants results in precocious leaf senescence. Together, these findings unveil an m6A-dependent regulatory module, SlYTH3-SlHDZIV2-SlATG5 that integrates RNA methylation and autophagy to modulate leaf senescence, providing mechanistic insights into epitranscriptomic control of plant aging.