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Severe cold, defined as a damaging cold beyond acclimation temperatures, has unique responses, but the signaling and evolution of these responses are not well understood. Production of oligogalactolipids, which is triggered by cytosolic acidification in Arabidopsis (Arabidopsis thaliana), contributes to survival in severe cold. Here, we investigated oligogalactolipid production in species from bryophytes to angiosperms. Production of oligogalactolipids differed within each clade, suggesting multiple evolutionary origins of severe cold tolerance. We also observed greater oligogalactolipid production in control samples than in temperature-challenged samples of some species. Further examination of representative species revealed a tight association between temperature, damage, and oligogalactolipid production that scaled with the cold tolerance of each species. Based on oligogalactolipid production and transcript changes, multiple angiosperm species share a signal of oligogalactolipid production initially described in Arabidopsis, namely cytosolic acidification. Together, these data suggest that oligogalactolipid production is a severe cold response that originated from an ancestral damage response that remains in many land plant lineages and that cytosolic acidification may be a common signaling mechanism for its activation.

Symbiotic nitrogen (N) fixation entails successful interaction between legume hosts and rhizobia that occur in specialized organs called nodules. N-fixing legumes have a higher demand for phosphorus (P) than legumes grown on mineral N. Medicago truncatula is an important model plant for characterization of effects of P deficiency at the molecular level. Hence, a study was carried out to address the alteration in metabolite levels of M. truncatula grown aeroponically and subjected to 4 weeks of P stress. First, GC-MS-based untargeted metabolomics initially revealed changes in the metabolic profile of nodules, with increased levels of amino acids and sugars and a decline in amounts of organic acids. Subsequently, LC-MS/MS was used to quantify these compounds including phosphorylated metabolites in the whole plant. Our results showed a drastic reduction in levels of organic acids and phosphorylated compounds in –P leaves, with a moderate reduction in –P roots and nodules. Additionally, sugars and amino acids were elevated in the whole plant under P deprivation. These findings provide evidence that N fixation in M. truncatula is mediated through a N feedback mechanism that in parallel is related to carbon and P metabolism.

The alcohol- and alkane-forming pathways in cuticular wax biosynthesis are well characterized in Arabidopsis. However, potential interactions between the two pathways remain unclear. Here, we reveal that mutation of CER4, the key gene in the alcohol-forming pathway, also led to a deficiency in the alkane-forming pathway in distal stems. To trace the connection between the two pathways, we characterized two homologs of fatty alcohol oxidase (FAO), FAO3 and FAO4b, which were highly expressed in distal stems and localized to the endoplasmic reticulum. The amounts of waxes from the alkane-forming pathway were significantly decreased in stems of fao4b and much lower in fao3 fao4b plants, indicative of an overlapping function for the two proteins in wax synthesis. Additionally, overexpression of FAO3 and FAO4b in Arabidopsis resulted in a dramatic reduction of primary alcohols and significant increases of aldehydes and related waxes. Moreover, expressing FAO3 or FAO4b led to significantly decreased amounts of C18–C26 alcohols in yeast co-expressing CER4 and FAR1. Collectively, these findings demonstrate that FAO3 and FAO4b are functionally redundant in suppressing accumulation of primary alcohols and contributing to aldehyde production, which provides a missing and long-sought-after link between these two pathways in wax biosynthesis.