Enhanced proteostasis, lipid remodeling, and nitrogen remobilization define barley flag leaf senescence

Abstract

Leaf senescence is a developmental process allowing nutrient remobilization to sink organs. We characterized flag leaf senescence at 7, 14 and 21 days past anthesis (dpa) in two near-isogenic barley lines varying in the allelic state of the HvNAM1 transcription factor gene, which influences senescence timing. Metabolomics and microscopy indicated that, as senescence progressed, thylakoid lipids were transiently converted to neutral lipids accumulating in lipid droplets. Senescing leaves also exhibited an accumulation of sugars including glucose, while nitrogen compounds (nucleobases, nucleotides, and amino acids) decreased. RNA-Seq analysis suggested lipid catabolism via β-oxidation and the glyoxylate cycle, producing carbon skeletons and feeding respiration in replacement of diminished carbon supply from photosynthesis. Comparison of the two barley lines highlighted a more prominent upregulation of Heat Stress Transcription Factor (HSF) and chaperone-encoding genes in the late-senescing line, suggesting a role for these genes in the control of leaf longevity. While numerous genes with putative roles in nitrogen remobilization were upregulated in both lines, several peptidases, nucleases and nitrogen transporters were more highly induced in the early-senescing line; this finding identifies processes and specific candidates which may affect nitrogen remobilization from senescing barley leaves, downstream of the HvNAM1 transcription factor.

Osmotic stress in roots drives lipoxygenase-dependent plastid remodeling through singlet oxygen production

“…Similarly, LOX3-RFP, a type 13 lipoxygenase, could clearly be traced to protrusions in the plastid membrane (Figure 7 A, bottom). In addition, changes in genes involved in the jasmonic acid pathway and massive plastid lipid remodeling were reported in barley flag-leaf senescence that could involve lipoxygenase activity (Cohen et al, 2022). Such scenario is consistent with lipoxygenase-dependent osmotic stress-induced plastid breakdown shown here.…”

Leaf Senescence Regulation Mechanism Based on Comparative Transcriptome Analysis in Foxtail Millet

“…KEGG enrichment analysis further revealed that genes related to lipid metabolism, including fatty acid and wax, were significantly up-regulated in SS under light conditions (Figure 5C). We expected that this might be due to lipid homeostasis and turnover being disrupted in SS foxtail millet during the developmental process, resulting in an accelerated senescence phenotype in response to environmental stress [42,43]. Furthermore, we observed that genes up-regulated in LS during DIS were largely associated with photosynthesis and chlorophyll metabolism (Figure 5B,D), which is in line with the beginnings of leaf senescence and might explain the conspicuous difference in the chlorophyll content and photosynthetic capacity between LS and SS [44,45].…”

Lipid droplets are versatile organelles involved in plant development and plant response to environmental changes

“…The presence of LDAP genes in the whole land plant kingdom (de Vries and Ischebeck, 2020) is consistent with the hypothesis that LDs may accumulate in leaves of every land plants. LDs accumulate in senescing leaves (Lersten et al, 2006;Brocard et al, 2017;Zhang et al, 2020;Cohen et al, 2022) where they are supposed to sequester galactolipid-derived FAs before conversion into phloem-mobile sucrose (Kaup et al, 2002). TAG synthesis has been demonstrated to occur in leaves, yet only a very limited TAG content was detected in Arabidopsis senescent leaves (Slocombe et al, 2009;Yang and Ohlrogge, 2009), suggesting this TAG accumulation is transient.…”