It is well known that salt stress has different effects on old and young tissues. However, it remains largely unexplored whether old and young tissues have different regulatory mechanism during ...adaptation of plants to salt stress. The aim of this study was to investigate whether salt stress has different effects on the ion balance and nitrogen metabolism in the old and young leaves of rice, and to compare functions of both organs in rice salt tolerance.
Rice protected young leaves from ion harm via the large accumulation of Na+ and Cl- in old leaves. The up-regulation of OsHKT1;1, OsHAK10 and OsHAK16 might contribute to accumulation of Na+ in old leaves under salt stress. In addition, lower expression of OsHKT1;5 and OsSOS1 in old leaves may decrease frequency of retrieving Na+ from old leaf cells. Under salt stress, old leaves showed higher concentration of NO3- content than young leaves. Up-regulation of OsNRT1;2, a gene coding nitrate transporter, might contribute to the accumulation of NO3- in the old leaves of salt stressed-rice. Salt stress clearly up-regulated the expression of OsGDH2 and OsGDH3 in old leaves, while strongly down-regulated expression of OsGS2 and OsFd-GOGAT in old leaves.
The down-regulation of OsGS2 and OsFd-GOGAT in old leaves might be a harmful response to excesses of Na+ and Cl-. Under salt stress, rice might accumulate Na+ and Cl- to toxic levels in old leaves. This might influence photorespiration process, reduce NH4+ production from photorespiration, and immediately down-regulate the expression of OsGS2 and OsFd-GOGAT in old leaves of salt stressed rice. Excesses of Na+ and Cl- also might change the pathway of NH4+ assimilation in old leaves of salt stressed rice plants, weaken GOGAT/GS pathway and elevate GDH pathway.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Effects of salt and alkali stresses on growth, osmotic adjustment and ionic balance of Suaeda glauca (Bge.), an alkali-resistant succulent halophyte, were compared. The results showed that alkali ...stress clearly inhibited the growth of S. glauca. Moreover, the concentrations of Na⁺ and K⁺ both increased with increasing salinity under both stresses, suggesting no competitive inhibition between absorptions of Na⁺ and K⁺. The mechanism underlying osmotic adjustment during salt stress was similar to alkali stress in shoots. The shared essential features were that organic acids, betaine and inorganic ions (dominated by Na⁺) mostly accumulated. On the other hand, the mechanisms governing ionic balance under both stresses were different. Under salt stress, S. glauca accumulated organic acids and inorganic anions to maintain the intracellular ionic equilibrium, but the anion contribution of inorganic ions was greater than that of organic acids. However, the concentrations of inorganic anions under alkali stress were significantly lower than those under salt stress of the same intensity, suggesting that alkali stress might inhibit uptake of anions, such as NO₃ ⁻ and H₂PO₄ ⁻. Under alkali stress, organic acids were the dominant factor in maintaining ionic equilibrium. The contribution of organic acids to anions was 74.1%, while that of inorganic anions was only 25.9%. S. glauca enhanced the synthesis of organic acids, dominated by oxalic acid, to compensate for the shortage of inorganic anions.
Hexaploid bread wheat (Triticum aestivum L., genome BBAADD) is generally more salt tolerant than its tetraploid wheat progenitor (Triticum turgidum L.). However, little is known about the ...physiological basis of this trait or about the relative contributions of allohexaploidization and subsequent evolutionary genetic changes on the trait development. Here, we compared the salt tolerance of a synthetic allohexaploid wheat (neo-6 x) with its tetraploid (T. turgidum ; BBAA) and diploid (Aegilops tauschii; DD) parents, as well as a natural hexaploid bread wheat (nat-6 x). We studied 92 morphophysiological traits and analyzed homeologous gene expression of a major salt-tolerance gene High-Affinity K ⁺ Transporter 1;5 (HKT1;5). We observed that under salt stress, neo-6 x exhibited higher fitness than both of its parental genotypes due to inheritance of favorable traits like higher germination rate from the 4 x parent and the stronger root Na ⁺ retention capacity from the 2 x parent. Moreover, expression of the D-subgenome HKT1;5 homeolog, which is responsible for Na ⁺ removal from the xylem vessels, showed an immediate transcriptional reprogramming following allohexaploidization, i.e., from constitutive high basal expression in Ae. tauschii (2 x) to salt-induced expression in neo-6 x . This phenomenon was also witnessed in the nat-6 x . An integrated analysis of 92 traits showed that, under salt-stress conditions, neo-6 x resembled more closely the 2 x than the 4 x parent, suggesting that the salt stress induces enhanced expressivity of the D-subgenome homeologs in the synthetic hexaploid wheat. Collectively, the results suggest that condition-dependent functionalization of the subgenomes might have contributed to the wide-ranging adaptability of natural hexaploid wheat.
Key message
Puccinellia tenuiflora
was domesticated for two years by growing it under non-saline conditions, providing epigenetic and biochemical insights into the initial domestication of extreme ...halophytes.
Some halophytes have economic value as crop species. The domestication of halophytes may offer hope in solving the problem of soil salinization. We domesticated a wild halophyte,
Puccinellia tenuiflora
, for two years by growing it under non-saline conditions in a greenhouse and used re-sequencing, genome-wide DNA methylation, biochemical, and transcriptome analyses to uncover the mechanisms underlying alterations in the halophyte’s tolerance to saline following domestication. Our results showed that non-saline domestication altered the methylation status for a number of genes and transposable elements, resulting in a much higher frequency of hypomethylation than hypermethylation. These modifications to DNA methylation were observed in many critical salinity-tolerance genes, particularly their promoter regions or transcriptional start sites. Twenty-nine potassium channel genes were hypomethylated and three were hypermethylated, suggesting that the DNA methylation status of potassium channel genes was influenced by domestication. The accelerated uptake of potassium is a major salinity tolerance characteristic of
P. tenuiflora
. We propose that modifications to the DNA methylation of potassium channel genes may be associated with the development of salinity tolerance in this species
.
By assessing whether non-saline domestication could change the salinity tolerance of
P. tenuiflora
, we demonstrated that non-saline domesticated plants are less tolerant to saline, which may be attributable to altered sucrose metabolism. DNA methylation and transposable elements may, therefore, be integrated into an environment-sensitive molecular engine that promotes the rapid domestication of
P. tenuiflora
to enable its use as a crop plant.
Kochia sieversiana (Pall.) C. A. M., a naturally alkali-resistant halophyte, was chosen as the test organism for our research. The seedlings of K. sieversiana were treated with varying (0-400 mM) ...salt stress (1:1 molar ratio of NaCl to Na₂SO₄) and alkali stress (1:1 molar ratio of NaHCO₃ to Na₂CO₃). The concentrations of various solutes in fresh shoots, including Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl-, SO ₄ ²- , NO ₃ - , H₂PO ₃ - , betaine, proline, soluble sugar (SS), and organic acid (OA), were determined. The water content (WC) of the shoots was calculated and the OA components were analyzed. Finally, the osmotic adjustment and ion balance traits in the shoots of K. sieversiana were explored. The results showed that the WC of K. sieversiana remained higher than 6 g g-¹ Dry weight (DW) even under the highest salt or alkali stress. At salinity levels >240 mM, proline concentrations increased dramatically, with rising salinity. We proposed that this was not a simple response to osmotic stress. The concentrations of Na⁺ and K⁺ all increased with increasing salinity, which implies that there was no competitive inhibition for absorption of either in K. sieversiana. Based on our results, the osmotic adjustment feature of salt stress was similar to that of alkali stress in the shoots of K. sieversiana. The shared essential features were that the shoots maintained a state of high WC, OA, Na⁺, K⁺ and other inorganic ions, accumulated largely in the vacuoles, and betaine, accumulated in cytoplasm. On the other hand, the ionic balance mechanisms under both stresses were different. Under salt stress, K. sieversiana accumulated OA and inorganic ions to maintain the intracellular ionic equilibrium, with close to equal contributions of OA and inorganic ions to anion. However, under alkali stress, OA was the dominant factor in maintaining ionic equilibrium. The contribution of OA to anion was as high as 84.2%, and the contribution of inorganic anions to anion was only 15.8%. We found that the physiological responses of K. sieversiana to salt and alkali stresses were unique, and that mechanisms existed in it that were different from other naturally alkali-resistant gramineous plants, such as Aneurolepidium chinense, Puccinellia tenuiflora.
Alkali stress is an important agricultural contaminant and has complex effects on plant metabolism. The aim of this study was to investigate whether the alkali stress has different effects on the ...growth, ion balance, and nitrogen metabolism in old and young leaves of rice plants, and to compare functions of both organs in alkali tolerance.
The results showed that alkali stress only produced a small effect on the growth of young leaves, whereas strongly damaged old leaves. Rice protected young leaves from ion harm via the large accumulation of Na(+) and Cl(-) in old leaves. The up-regulation of OsHKT1;1, OsAKT1, OsHAK1, OsHAK7, OsHAK10 and OsHAK16 may contribute to the larger accumulation of Na(+) in old leaves under alkali stress. Alkali stress mightily reduced the NO(3)(-) contents in both organs. As old leaf cells have larger vacuole, under alkali stress these scarce NO(3)(-) was principally stored in old leaves. Accordingly, the expression of OsNRT1;1 and OsNRT1;2 in old leaves was up-regulated by alkali stress, revealing that the two genes might contribute to the accumulation of NO(3)(-) in old leaves. NO(3)(-) deficiency in young leaves under alkali stress might induce the reduction in OsNR1 expression and the subsequent lacking of NH(4)(+), which might be main reason for the larger down-regulation of OsFd-GOGAT and OsGS2 in young leaves.
Our results strongly indicated that, during adaptation of rice to alkali stress, young and old leaves have distinct mechanisms of ion balance and nitrogen metabolism regulation. We propose that the comparative studies of young and old tissues may be important for abiotic stress tolerance research.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Halophytes and glycophytes exhibit clear differences in their tolerance to high levels of salinity. The genetic mechanisms underlying this differentiation, however, remain unclear. To unveil these ...mechanisms, we surveyed the evolution of salinity-tolerant gene families through comparative genomic analyses between the model halophyte
and glycophytic Gramineae plants, and compared their transcriptional and physiological responses to salinity stress. Under salinity stress, the K
concentration in the root was slightly enhanced in
, but it was greatly reduced in the glycophytic Gramineae plants, which provided a physiological explanation for differences in salinity tolerance between
and these glycophytes. Interestingly, several K
uptake gene families from
experienced family expansion and positive selection during evolutionary history. This gene family expansion and the elevated expression of K
uptake genes accelerated K
accumulation and decreased Na
toxicity in
roots under salinity stress. Positively selected
K
uptake genes may have evolved new functions that contributed to development of
salinity tolerance. In addition, the expansion of the gene families involved in pentose phosphate pathway, sucrose biosynthesis, and flavonoid biosynthesis assisted the adaptation of
to survival under high salinity conditions.
Puccinellia tenuiflora, a forage grass, is considered a model halophyte given its strong tolerance for multiple stress conditions and its close genetic relationship with cereals. This halophyte has ...enormous values for improving our understanding of salinity tolerance mechanisms. The genetic information of P. tenuiflora also is a potential resource that can be used for improving the salinity tolerance of cereals.
Here, we sequenced and assembled the P. tenuiflora genome (2n = 14) through the combined strategy of Illumina, PacBio, and 10× genomic technique. We generated 43.2× PacBio long reads, 123.87× 10× genomic reads, and 312.6× Illumina reads. Finally, we assembled 2638 scaffolds with a total size of 1.107 Gb, contig N50 of 117 kb, and scaffold N50 of 950 kb. We predicted 39,725 protein-coding genes, and identified 692 tRNAs, 68 rRNAs, 702 snRNAs, 1376 microRNAs, and 691 Mb transposable elements.
We deposited the genome sequence in NCBI and the Genome Warehouse in National Genomics Data Center. Our work may improve current understanding of plant salinity tolerance, and provides extensive genetic resources necessary for improving the salinity and drought tolerance of cereals.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Most studies of crop salinity tolerance are conducted under short-term stress condition within one growth stage. Understanding of the mechanisms of crop response to long-term salinity stress (LSS) is ...valuable for achieving the improvement of crop salinity tolerance. In the current study, we exposed allohexaploid wheat seeds to LSS conditions from germination stage to young seedling stage for 30 days. To elucidate the adaptive strategy of allohexaploid wheat to LSS, we analyzed chloroplast ultrastructure, leaf anatomy, transcriptomic profiling and concentrations of plant hormones and organic compatible solutes, comparing stressed and control plants.
Transcriptomic profiling and biochemical analysis showed that energy partitioning between general metabolism maintenance and stress response may be crucial for survival of allohexaploid wheat under LSS. Under LSS, wheat appeared to shift energy from general maintenance to stress response through stimulating the abscisic acid (ABA) pathway and suppressing gibberellin and jasmonic acid pathways in the leaf. We further distinguished the expression status of the A, B, and D homeologs of any gene triad, and also surveyed the effects of LSS on homeolog expression bias for salinity-tolerant triads. We found that LSS had similar effects on expression of the three homeologs for most salinity-tolerant triads. However, in some of these triads, LSS induced different effects on the expression of the three homeologs.
The shift of the energy from general maintenance to stress response may be important for wheat LSS tolerance. LSS influences homeolog expression bias of salinity-tolerant triads.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
It is known that hexaploid common wheat (Triticum aestivum L.) has stronger adaptability to many stressful environments than its tetraploid wheat progenitor. However, the physiological basis and ...evolutionary course to acquire these enhanced adaptabilities by common wheat remain understudied. Here, we aimed to investigate whether and by what means tolerance to low-nitrogen manifested by common wheat may emerge immediately following allohexaploidization.
We compared traits related to nitrogen (N) metabolism in a synthetic allohexaploid wheat (neo-6×, BBAADD) mimicking natural common wheat, together with its tetraploid (BBAA, 4×) and diploid (DD, 2×) parents. We found that, under low nitrogen condition, neo-6× maintained largely normal photosynthesis, higher shoot N accumulation, and better N assimilation than its 4× and 2× parents. We showed that multiple mechanisms underlie the enhanced tolerance to N-deficiency in neo-6×. At morphological level, neo-6× has higher root/shoot ratio of biomass than its parents, which might be an adaptive growth strategy as more roots feed less shoots with N, thereby enabling higher N accumulation in the shoots. At electrophysiological level, H
efflux in neo-6× is higher than in its 4× parent. A stronger H
efflux may enable a higher N uptake capacity of neo-6×. At gene expression level, neo-6× displayed markedly higher expression levels of critical genes involved in N uptake than both of its 4× and 2× parents.
This study documents that allohexaploid wheat can attain immediate higher tolerance to N-deficiency compared with both of its 4× and 2× parents, and which was accomplished via multiple mechanisms.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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