HLS1 interacts with ATG8 to negatively regulate the ABS3-mediated plant senescence pathway

In Arabidopsis, late endosome-localized ABNORMAL SHOOT 3 (ABS3) promotes senescence through a direct interaction with AUTOPHAGY8 (ATG8). However, the molecular mechanisms underlying the regulation of the ABS3-mediated senescence pathway are not well understood. Here, we report that HOOKLESS 1 (HLS1) acts as a negative regulator of plant senescence and the ABS3-mediated senescence pathway. We identify the localizations of HLS1 at the plasma membrane and endosomes in addition to the nucleus. Mechanistically, non-nucleus-localized HLS1 directly interacts with ATG8, attenuates the ABS3-ATG8 interaction, and inhibits the vacuolar degradation of ABS3, thereby antagonizing the senescence-promoting role of ABS3. Additionally, we show that the stability of HLS1 itself is negatively regulated during carbon deprivation-induced senescence. Finally, we find that HLS1 homologs in both Arabidopsis and wheat play a conserved role in senescence regulation. In summary, our findings show the functional link between HLS1, ABS3, and ATG8 in plant senescence regulation.