Pro-inflammatory immune responses are necessary for effective pathogen clearance, but cause severe tissue damage if not shut down in a timely manner^1,2. Excessive complement and IFN-γ-associated responses are known drivers of immunopathogenesis³ and are among the most highly induced immune programs in hyper-inflammatory SARS-CoV2 lung infection⁴. The molecular mechanisms that govern orderly shutdown and retraction of these responses remain poorly understood. Here, we show that complement triggers contraction of IFN-γ producing CD4⁺ T helper (Th) 1 cell responses by inducing expression of the vitamin D (VitD) receptor (VDR) and CYP27B1, the enzyme that activates VitD, permitting T cells to both activate and respond to VitD. VitD then initiates the transition from pro-inflammatory IFN-γ⁺ Th1 cells to suppressive IL-10⁺ Th1 cells. This process is primed by dynamic changes in the epigenetic landscape of CD4⁺ T cells, generating superenhancers and recruiting c-JUN and BACH2, a key immunoregulatory transcription factor^5–7. Accordingly, cells in psoriatic skin treated with VitD increased BACH2 expression, and BACH2 haplo-insufficient CD4⁺ T cells were defective in IL-10 production. As proof-of-concept, we show that CD4⁺ T cells in the bronchoalveolar lavage fluid (BALF) of patients with COVID-19 are Th1-skewed and that VDR is among the top regulators of genes induced by SARS-CoV2. Importantly, genes normally down-regulated by VitD were de-repressed in CD4⁺ BALF T cells of COVID-19, indicating that the VitD-driven shutdown program is impaired in this setting. The active metabolite of VitD, alfacalcidol, and cortico-steroids were among the top predicted pharmaceuticals that could normalize SARS-CoV2 induced genes. These data indicate that adjunct therapy with VitD in the context of other immunomodulatory drugs may be a beneficial strategy to dampen hyperinflammation in severe COVID-19.

Summary: The Arabidopsis FATTY ACID ELONGATION1 (FAE1) gene encodes a putative seed‐specific condensing enzyme. It is the first of four enzyme activities that comprise the microsomal fatty acid elongase (FAE) involved in the biosynthesis of very‐long‐chain fatty acids (VLCFAs). FAE1 has been expressed in yeast and in tissues of Arabidopsis and tobacco, where significant quantities of VLCFAs are not found. The introduction of FAE1 alone in these systems is sufficient for the production of VLCFAs, for wherever FAE1 was expressed, VLCFAs accumulated. These results indicate that FAE1 is the rate‐limiting enzyme for VLCFA biosynthesis in Arabidopsis seed, because introduction of extra copies of FAE1 resulted in higher levels of the VLCFAs. Furthermore, the condensing enzyme is the activity of the elongase that determines the acyl chain length of the VLCFAs produced. In contrast, it appears that the other three enzyme activities of the elongase are found ubiquitously throughout the plant, are not rate‐limiting and play no role in the control of VLCFA synthesis. The ability of yeast containing FAE1 to synthesize VLCFAs suggests that the expression and the acyl chain length specificity of the condensing enzyme, along with the apparent broad specificities of the other three FAE activities, may be a universal eukaryotic mechanism for regulating the amounts and acyl chain length of VLCFAs synthesized.

Land plants secrete a layer of wax onto their aerial surfaces that is essential for survival in a terrestrial environment. This wax is composed of long-chain, aliphatic hydrocarbons derived from very-long-chain fatty acids (VLCFAs). Using the Arabidopsis expressed sequence tag database, we have identified a gene, designated CUT1, that encodes a VLCFA condensing enzyme required for cuticular wax production. Sense suppression of CUT1 in transgenic Arabidopsis plants results in waxless (eceriferum) stems and siliques as well as conditional male sterility. Scanning electron microscopy revealed that this was a severe waxless phenotype, because stems of CUT1-suppressed plants were completely devoid of wax crystals. Furthermore, chemical analyses of waxless plants demonstrated that the stem wax load was reduced to 6 to 7% of wild-type levels. This value is lower than that reported for any of the known eceriferum mutants. The severe waxless phenotype resulted from the downregulation of both the decarbonylation and acyl reduction wax biosynthetic pathways. This result indicates that CUT1 is involved in the production of VLCFA precursors used for the synthesis of all stem wax components in Arabidopsis. In CUT1-suppressed plants, the C24 chain-length wax components predominate, suggesting that CUT1 is required for elongation of C24 VLCFAs. The unique wax composition of CUT1-suppressed plants together with the fact that the location of CUT1 on the genetic map did not coincide with any of the known ECERIFERUM loci suggest that we have identified a novel gene involved in wax biosynthesis. CUT1 is currently the only known gene with a clearly established function in wax production.

Summary: We have investigated the relationship between seed dormancy and abscisic acid (ABA) metabolism in the monocot barley and the dicot Arabidopsis. Whether dormant (D) or non‐dormant (ND), dry seed of Arabidopsis and embryos of dry barley grains all had similarly high levels of ABA. ABA levels decreased rapidly upon imbibition, although they fell further in ND than in D. Gene expression profiles were determined in Arabidopsis for key ABA biosynthetic [the 9‐cis epoxycarotenoid dioxygenasegene family] and ABA catabolic [the ABA 8′‐hydroxylase gene family (CYP707A)] genes. Of these, only the AtCYP707A2 gene was differentially expressed between D and ND seeds, being expressed to a much higher level in ND seeds. Similarly, a barley CYP707 homologue, (HvABA8′OH‐1) was expressed to a much higher level in embryos from ND grains than from D grains. Consistent with this, in situ hybridization studies showed HvABA8′OH‐1 mRNA expression was stronger in embryos from ND grains. Surprisingly, the signal was confined in the coleorhiza, suggesting that this tissue plays a key role in dormancy release. Constitutive expression of a CYP707A gene in transgenic Arabidopsis resulted in decreased ABA content in mature dry seeds and a much shorter after‐ripening period to overcome dormancy. Conversely, mutating the CYP707A2 gene resulted in seeds that required longer after‐ripening to break dormancy. Our results point to a pivotal role for the ABA 8′‐hydroxylase gene in controlling dormancy and that the action of this enzyme may be confined to a particular organ as in the coleorhiza of cereals.

Currently, there are very few loss-of-function mutations in micro-RNA genes. Here, we characterize two members of the Arabidopsis MIR159 family, miR159a and miR159b, that are predicted to regulate the expression of a family of seven transcription factors that includes the two redundant GAMYB-like genes, MYB33 and MYB65 . Using transfer DNA (T-DNA) insertional mutants, we show that a mir159ab double mutant has pleiotropic morphological defects, including altered growth habit, curled leaves, small siliques, and small seeds. Neither mir159a nor mir159b single mutants displayed any of these traits, indicating functional redundancy. By using reporter-gene constructs, it appears that MIR159a and MIR159b are transcribed almost exclusively in the cells in which MYB33 is repressed, as had been previously determined by comparison of MYB33 and mMYB33 (an miR159-resistant allele of MYB33 ) expression patterns. Consistent with these overlapping transcriptional domains, MYB33 and MYB65 expression levels were elevated throughout mir159ab plants. By contrast, the other five GAMYB-like family members are transcribed predominantly in tissues where miR159a and miR159b are absent, and consequently their expression levels are not markedly elevated in mir159ab . Additionally, mMYB33 transgenic plants can phenocopy the mir159ab phenotype, suggesting that its phenotype is explained by deregulated expression of the redundant gene pair MYB33 and MYB65 . This prediction was confirmed; the pleiotropic developmental defects of mir159ab are suppressed through the combined mutations of MYB33 and MYB65 , demonstrating the narrow and specific target range of miR159a and miR159b.