Autophagy Influences Maize Endosperm Maturation by Dampening Oxidative Stress and Promoting Mitochondrial Clearance

The selective turnover of macromolecules by autophagy provides an essential homeostatic mechanism for recycling intercellular constituents, and for removing superfluous and damaged organelles, lipids, and proteins. To better understand how autophagy impacts seed maturation and nutrient storage, we studied maize (Zea mays) endosperm development via an integrated multi-omics approach using mutants impacting the core macroautophagy factor ATG12 required for autophagosome assembly. Surprisingly, the mutant endosperm accumulated starch and the Zein storage proteins normally, further supporting an alternative non-autophagic route for their sequestration. However, the tissue developed a substantially altered metabolome, especially for compounds related to oxidative stress, including increases in cystine, dehydroascorbate, cys-glutathione disulfide, glucarate and galactarate, and decreases in peroxide and the anti-oxidant glutathionine. While mild changes in the associated transcriptome were seen, a strongly altered proteome was evident in the atg12 mutants, especially for increased levels of mitochondrial proteins in the absence of mRNA changes. Although less mitochondria were seen cytologically, a heightened number appeared dysfunctional based on the accumulation of dilated cristae, consistent with attenuated mitophagy. Collectively, our results confirm that macroautophagy has little role in packing storage compounds during maize endosperm development, but likely helps protect against oxidative stress and clear unneeded/dysfunctional mitochondria during tissue maturation.