Salinity tolerance comes from genes that limit the rate of salt uptake from the soil and the transport of salt throughout the plant, adjust the ionic and osmotic balance of cells in roots and shoots, and regulate leaf development and the onset of senescence. This review lists some candidate genes for salinity tolerance, and draws together hypotheses about the functions of these genes and the specific tissues in which they might operate. Little has been revealed by gene expression studies so far, perhaps because the studies are not tissue-specific, and because the treatments are often traumatic and unnatural. Suggestions are made to increase the value of molecular studies in identifying genes that are important for salinity tolerance.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.2005.01487.x

Genes and salt tolerance: bringing them together.

https://www.cell.com/trends/plant-science/pdf/S1360-1385(10)00032-4.pdf

WRKY transcription factors.

Dynasore, a Cell-Permeable Inhibitor of Dynamin

Ageing results from complex genetically and epigenetically programmed processes that are elicited in part by noxious or stressful events that cause programmed cell death Here, we report that administration of spermidine, a natural polyamine whose intracellular concentration declines during human ageing, markedly extended the lifespan of yeast, flies and worms, and human immune cells In addition, spermidine administration potently inhibited oxidative stress in ageing mice In ageing yeast, spermidine treatment triggered epigenetic deacetylation of histone H3 through inhibition of histone acetyltransferases (HAT), suppressing oxidative stress and necrosis Conversely, depletion of endogenous polyamines led to hyperacetylation, generation of reactive oxygen species, early necrotic death and decreased lifespan The altered acetylation status of the chromatin led to significant upregulation of various autophagy-related transcripts, triggering autophagy in yeast, flies, worms and human cells Finally, we found that enhanced autophagy is crucial for polyamine-induced suppression of necrosis and enhanced longevity

Induction of autophagy by spermidine promotes longevity

Protein phosphorylation in regulation of photosynthesis

Leaf senescence, the final step of leaf development, involves extensive reprogramming of gene expression. Here, we show that these processes include discrete changes of epigenetic indexing, as well as global alterations in chromatin organization. During leaf senescence, the interphase nuclei show a decondensation of chromocenter heterochromatin, and changes in the nuclear distribution of the H3K4me2, H3K4me3, and the H3K27me2 and H3K27me3 histone modification marks that index active and inactive chromatin, respectively. Locus-specific epigenetic indexing was studied at the WRKY53 key regulator of leaf senescence. During senescence, when the locus becomes activated, H3K4me2 and H3K4me3 are significantly increased at the 5' end and at coding regions. Impairment of these processes is observed in plants overexpressing the SUVH2 histone methyltransferase, which causes ectopic heterochromatization. In these plants the transcriptional initiation of WRKY53 and of the senescence-associated genes SIRK, SAG101, ANAC083, SAG12 and SAG24 is inhibited, resulting in a delay of leaf senescence. In SUVH2 overexpression plants, significant levels of H3K27me2 and H3K27me3 are detected at the 5'-end region of WRKY53, resulting in its transcriptional repression. Furthermore, SUVH2 overexpression inhibits senescence-associated global changes in chromatin organization. Our data suggest that complex epigenetic processes control the senescence-specific gene expression pattern.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.0960-7412.2009.03782.x

Epigenetic programming via histone methylation at WRKY53 controls leaf senescence in Arabidopsis thaliana.

Changes in the function and composition of the photosynthetic apparatus were analysed during maturation and senescence of barley (Hordeum vulgare L.) flag leaves under field conditions. At about 8 d post-anthesis, photosynthetic capacity, measured as oxygen evolution under light-saturating conditions, and the D 1 protein level started to decrease. At about 14 d post-anthesis, the pigment content, photosystem II efficiency (F v /F m ) and levels of cytochrome f and the large subunit of ribulose-1,5-bis-phosphate carboxylase started to decline. The levels of cytochrome b559 and the small subunit of ribulose-1,5-bis-phosphate carboxylase decreased later, at about 22 d post-anthesis. High levels of the light-harvesting complex of photosystem II were still detectable at an even later stage of senescence, at 26 d post-anthesis. There were also differences in the kinetics of the declines in the levels of transcripts coding for components of the photosynthetic apparatus. rbcS mRNA abundance had already decreased when flag leaves reached their final lengths, at about 4 d post-anthesis, whereas levels of psbA and petC transcripts did not decrease until 16 d post-anthesis. In contrast, a senescence-related transcript, pHvS40 (Becker & Apel 1993), accumulated in the flag leaves 14 d post-anthesis. Several senescence-related processes which differ in their kinetics are described. The interrelationships among these processes and their regulation are discussed.

Functional and molecular changes in the photosynthetic apparatus during senescence of flag leaves from field‐grown barley plants

Epigenetic programming via histone methylation at WRKY53 controls leaf senescence in Arabidopsis thaliana: Epigenetic control of leaf senescence

Leaf senescence is a developmentally controlled process, which is additionally modulated by a number of adverse environmental conditions. Nitrogen shortage is a well-known trigger of precocious senescence in many plant species including crops, generally limiting biomass and seed yield. However, leaf senescence induced by nitrogen starvation may be reversed when nitrogen is resupplied at the onset of senescence. Here, the transcriptomic, hormonal, and global metabolic rearrangements occurring during nitrogen resupply-induced reversal of senescence in Arabidopsis thaliana were analysed. The changes induced by senescence were essentially in keeping with those previously described; however, these could, by and large, be reversed. The data thus indicate that plants undergoing senescence retain the capacity to sense and respond to the availability of nitrogen nutrition. The combined data are discussed in the context of the reversibility of the senescence programme and the evolutionary benefit afforded thereby. Future prospects for understanding and manipulating this process in both Arabidopsis and crop plants are postulated.

Reversal of senescence by N resupply to N-starved Arabidopsis thaliana: transcriptomic and metabolomic consequences

Breakdown of leaf proteins, particularly chloroplast proteins, is a massive process in senescing leaves. In spite of its importance in internal N recycling, the mechanism(s) and the enzymes involved are largely unknown. Senescence-associated vacuoles (SAVs) are small, acidic vacuoles with high cysteine peptidase activity. Chloroplast-targeted proteins re-localize to SAVs during senescence, suggesting that SAVs might be involved in chloroplast protein degradation. SAVs were undetectable in mature, non-senescent tobacco leaves. Their abundance, visualized either with the acidotropic marker Lysotracker Red or by green fluorescent protein (GFP) fluorescence in a line expressing the senescence-associated cysteine protease SAG12 fused to GFP, increased during senescence induction in darkness, and peaked after 2-4 d, when chloroplast dismantling was most intense. Increased abundance of SAVs correlated with higher levels of SAG12 mRNA. Activity labelling with a biotinylated derivative of the cysteine protease inhibitor E-64 was used to detect active cysteine proteases. The two apparently most abundant cysteine proteases of senescing leaves, of 40kDa and 33kDa were detected in isolated SAVs. Rubisco degradation in isolated SAVs was completely blocked by E-64. Treatment of leaf disks with E-64 in vivo substantially reduced degradation of Rubisco and leaf proteins. Overall, these results indicate that SAVs contain most of the cysteine protease activity of senescing cells, and that SAV cysteine proteases are at least partly responsible for the degradation of stromal proteins of the chloroplast.

In vivo inhibition of cysteine proteases provides evidence for the involvement of ‘senescence-associated vacuoles’ in chloroplast protein degradation during dark-induced senescence of tobacco leaves

Klaus Humbeck

Papers

Epigenetic programming via histone methylation at WRKY53 controls leaf senescence in Arabidopsis thaliana.

Functional and molecular changes in the photosynthetic apparatus during senescence of flag leaves from field‐grown barley plants

Epigenetic programming via histone methylation at WRKY53 controls leaf senescence in Arabidopsis thaliana: Epigenetic control of leaf senescence

Reversal of senescence by N resupply to N-starved Arabidopsis thaliana: transcriptomic and metabolomic consequences

In vivo inhibition of cysteine proteases provides evidence for the involvement of ‘senescence-associated vacuoles’ in chloroplast protein degradation during dark-induced senescence of tobacco leaves