Arabidopsis Apoplast TET8 Positively Correlates to Leaf Senescence and Double Mutants are Delayed in Leaf Senescence.

Extracellular vesicles (EVs) are membrane-bound exosomes secreted into the apoplast. Two distinct populations of EVs have been described in Arabidopsis: PEN1-associated and TET8-associated. We previously noted early leaf senescence in the single and double mutant. Both PEN1 and PEN3 are abundant in EV proteomes suggesting EVs might regulate leaf senescence in soil-grown plants. We observed that TET8 is more abundant in the apoplast of early senescing and mutant rosettes and in older WT rosettes. The increase in apoplast TET8 in the mutant did not correspond to increased mRNA levels. In addition, apoplast TET8 was more abundant in the early leaf senescence mutant, meaning the increase in apoplast TET8 protein during leaf senescence is not dependent on or . Genetic analysis showed a significant delay in leaf senescence in double mutants after six weeks of growth suggesting that these two tetraspanin paralogs operate additively and are positive regulators of leaf senescence. This is opposite of the effect of and mutants that show early senescence and suggest PEN1 to be a negative regulator of leaf senescence. Our work provides initial support that PEN1-associated EVs and TET8-associated EVs may have opposite effects on soil-grown plants undergoing age-related leaf senescence.