Salt stress has the most severe impact on plant growth and development, including seed germination. However, little is known about the mechanism of NR (nitrate reductase)-associated nitric oxide (NO) ...regulates salt tolerance during seed germination in rice. Herein, we shown that inhibition of seed germination by salt stress was significantly impaired by sodium nitroferricyanide (SNP), a NO donor. Then a triple mutant,
, was generated. Results shown that germination of triple mutants were delayed and were much more sensitive to salt stress than WT plant, which can be rescued by application of SNP. qPCR analysis revealed that expressions of abscisic acid (ABA) catabolism gene,
, was suppressed in triple mutants under salt stress, resulting in an elevated ABA content. Similar to SNP, application of nitrate also rescued seed germination under salt stress, which, however, was blocked in the triple mutants. Further study revealed that a nitrate responsive transcript factor,
, was induced by salt stress, which thus up-regulates the expression of
and NR activity, resulting in promoted salt tolerance during seed germination. In addition, nitrate-mediated salt tolerance was impaired in mutant of
, a target gene for NLP2. Transient trans-activation assays further revealed NLP2 can significantly activate the expression of
and
, suggesting that NLP2 activates expression of ABA catabolism gene directly or indirectly via NR-associated NO. Taken together, our results demonstrate that NLP2-NR associated NO was involved in salt response by increasing ABA catabolism during seed germination and highlight the importance of NO for stress tolerance of plants.
Zinc (Zn)-regulated and iron (Fe)-regulated transporter-like proteins (ZIP) are key players involved in the accumulation of cadmium (Cd) and Zn in plants.
X.H. Guo et S.B. Zhou ex L.H. Wu (
) is a ...Crassulaceae Cd/Zn hyperaccumulator found in China, but the role of ZIPs in
remains largely unexplored. Here, we identified 12 members of
family genes by transcriptome analysis in
and cloned the
gene with functional analysis. The expression of
in roots was higher than that in the shoots, and Cd stress significantly decreased its expression in the roots but increased its expression in leaves. Protein sequence characteristics and structural analysis showed that the content of alanine and leucine residues in the SpZIP2 sequence was higher than other residues, and several serine, threonine and tyrosine sites can be phosphorylated. Transmembrane domain analysis showed that SpZIP2 has the classic eight transmembrane regions. The evolutionary analysis found that SpZIP2 is closely related to OsZIP2, followed by AtZIP11, OsZIP1 and AtZIP2. Sequence alignment showed that most of the conserved sequences among these members were located in the transmembrane regions. A further metal sensitivity assay using yeast mutant Δ
showed that the expression of
increased the sensitivity of the transformants to Cd but failed to change the resistance to Zn. The subsequent ion content determination showed that the expression of
increased the accumulation of Cd in yeast. Subcellular localization showed that SpZIP2 was localized to membrane systems, including the plasma membrane and endoplasmic reticulum. The above results indicate that
member
participates in the uptake and accumulation of Cd into cells and might contribute to Cd hyperaccumulation in
.
Nitrogen and brassinosteroids (BRs) play a vital role in modulating the growth, development, and yield of rice. However, the influences of BRs on nitrogen assimilation and metabolism in rice are not ...fully understood. In this study, we analyzed the impact of BRs on nitrogen utilization in rice using the indica variety ‘Zhongjiazao 17’ and the japonica variety ‘Nipponbare’ in hydroponic conditions. The results showed that BR treatment could efficiently elevate nitrate and ammonium nitrogen accumulation in both shoots and roots. Furthermore, some genes involved in the uptake of nitrate and ammonium in roots were stimulated by BRs, though we noted subtle variances between the two rice cultivars. Moreover, BRs augmented the activity of nitrate reductase (NR) and glutamine synthetase (GS) in roots, along with NR in shoots. Interestingly, BRs also spiked the total free amino acid content in both the shoots and roots. Gene expression analysis uncovered a robust induction by BRs of NR genes and GS-related genes in the roots of both ‘Nipponbare’ and ‘Zhongjiazao 17’. Collectively, our data suggest that BRs significantly enhance the accumulation of both nitrate and ammonium in rice and trigger a series of reactions related to nitrogen utilization.
Saline‐alkali stress is one of the major abiotic stresses that severely affect rice yield. However, the mechanism by which saline‐alkali stress regulates grain filling in rice is still unclear. In ...this study, Oryza sativa L. spp. Indica cultivar Chaoyou1000 (C1000) was exposed to post‐anthesis saline‐alkali conditions at 6 days after anthesis, which significantly reduced the grain weight by suppressing the accumulation of starch and non‐structural carbohydrates in grains. Further analysis found that 1‐aminocyclopropane‐1‐carboxylate (ACC), a precursor for ethylene, was increased by saline‐alkali treatment. qRT‐PCR results showed that several key genes involved in ethylene biosynthesis, including the OsACS and OsACO genes, were upregulated in saline‐alkali‐treated grains. In addition, genes involved in the ethylene signalling pathway were also induced by saline‐alkali stress. Exogenous ethylene application reduced grain weight and both starch and NSC contents in grains of C1000, suggesting that saline‐alkali‐induced ethylene has a negative effect on grain filling. Furthermore, the gene expression levels of OsSUS, OsAGPL, OsAGPS, OsSSI and OsSSIIIa, which are key genes in the starch biosynthesis pathway, were downregulated in saline‐alkali‐treated grains. In agreement, assays on these enzymes further revealed that saline‐alkali stress decreased the activities of sucrose synthase (SUS), adenosine diphosphate glucose pyrophosphorylase (AGP) and starch synthase (StS). Together, our results indicated that saline‐alkali stress suppressed the enzyme activities involved in the conversion of sucrose to starch by elevating ethylene production, which led to inhibition of grain filling.
Post‐anthesis saline‐alkali stress increases ethylene production by upregulating gene expression of ethylene biosynthesis, which thus activates ethylene signalling transduction in rice grains. Gene expression and enzyme activities for starch accumulation in rice grains are both decreased by elevated ethylene, resulting in decreased efficiency of starch biosynthesis and eventually lower grain weight.
Isolating the genes responsible for cadmium (Cd) accumulation and tolerance in oilseed rape and uncovering their functional mechanism is of great significance for guiding genetic improvement to cope ...with heavy metal pollution. In this study, we screened the cDNA library of Brassica napus cv. Westar using a yeast genetic complementation system and isolated BnMT2-22a, BnMT2-22b and BnMT3b, which can mediate Cd tolerance in yeast. They all have two cysteine-rich domains in their sequence. Ectopic expression of these MTs demonstrated that all of them enhanced Cd and Cu tolerance in yeast, but had no effect on Mn and Zn tolerance. The fusion of the red fluorescent protein mRFP did not affect their function in mediating Cd tolerance, and using these functional fusion proteins we observed that they were all localized in cytosol. Meanwhile, their expression in yeast did not affect the accumulation of Cd in the yeast transformants. Gene expression analyses found that BnMT2-22a, BnMT2-22b and BnMT3b were all induced by Cd in roots, and BnMT3b was also significantly induced in shoots. These results indicate that the genes BnMT2-22a, BnMT2-22b and BnMT3b isolated with cDNA library screening can mediate Cd tolerance, and they may detoxify Cd via cytosolic chelation.
A digital background calibration scheme for calibrating the linear, third-order, and fifth-order nonlinear gain errors of the residue amplifiers (RAs) in pipelined ADCs is proposed. By alternating ...injecting three pseudo-random binary sequences (PRBS) with designated weights to the RA through the sub-DAC, multiple correlations of the nonlinearity-corrected backend ADC's outputs and the injected PRBS signals are computed by digital circuits to estimate the calibration parameters according to the proposed multiple correlation estimation (MCE) method. Three least-mean-square (LMS) loops are used to acquire and track the optimal values of the calibration parameters in background so as to vanish all the errors in the ADC's output. Simulation results of a 14-bit pipelined ADC show the proposed calibration scheme improves the SNDR of the ADC from 31.2 dB to 80.4 dB. The proposed calibration scheme relaxes the design requirements of the RAs, making it well suit the design in advanced technology.
In rice (
), a specific temporary source organ, the stem, is important for grain filling, and moderate soil drying (MD) enhanced carbon reserve flow from stems to increase grain yield. The dynamics ...and biological relevance of DNA methylation in carbon reserve remobilization during grain filling are unknown. Here, we generated whole-genome single-base resolution maps of the DNA methylome in the stem. During grain filling under MD, we observed an increase in DNA methylation of total cytosines, with more hypomethylated than hypermethylated regions. Genes responsible for DNA methylation and demethylation were up-regulated, suggesting that DNA methylation changes in the stem were regulated by antagonism between DNA methylation and demethylation activity. In addition, methylation in the CG and CHG contexts was negatively associated with gene expression, while that in the CHH context was positively associated with gene expression. A hypermethylated/up-regulated transcription factor of
inhibited
expression and possibly enhanced
expression, promoting subsequent starch degradation in rice stems under MD treatment. In addition, a hypermethylated/down-regulated transcription factor of
was predicted to interact with, and thereby decrease the expression of, abscisic acid 8'-hydroxylase1, thus increasing abscisic acid concentration under MD treatment. Our findings provide insight into the DNA methylation dynamics in carbon reserve remobilization of rice stems, demonstrate that MD increased this remobilization, and suggest a link between DNA methylation and gene expression in rice stems during grain filling.
Carbohydrate accumulation in inferior grains in rice panicles subjected to moderate post-anthesis water stress is regulated by NAC transcription factors that activate the expression of WAXY.
Abstract
...Moderate soil drying imposed at the post-anthesis stage significantly increases starch accumulation in inferior grains of rice, but how this process is regulated at the level of gene expression remains unclear. In this study, we applied moderate drying (MD) treatments to the soil at the post-anthesis stage and followed the dynamics of the conversion process of soluble sugars to starch in inferior grains using RNA-seq analysis. An elevated level of ABA induced by MD was consistently associated with down-regulation of ABA8ox2, suggesting that lower expression of this gene may be responsible for the higher ABA content, potentially resulting in better filling in inferior grains. In addition, MD treatments up-regulated genes encoding five key enzymes involved sucrose-to-starch conversion and increased the activities of enzymes responsible for soluble-sugar reduction and starch accumulation in inferior grains. Differentially expressed transcription factors, including NAC, GATA, WRKY, and M-type MADS, were predicted to interact with other proteins in mediating filling of inferior grains as a response to MD. Transient expression analysis showed that NAC activated WAXY expression by binding to its promoter, indicating that NAC played a key role in starch synthesis of inferior grains under MD treatment. Our results provide new insights into the molecular mechanisms that regulate grain filling in inferior grains of rice under moderate soil drying.
Seed dormancy and germination determine the beginning of the life cycle of plants, and the phytohormone ABA plays a crucial role in regulation of seed dormancy and germination. However, the upstream ...regulatory mechanism of ABA metabolism during dormancy releasing is still remain elusive. In this paper, we present a novel mechanism of OsNAC2 in controlling ABA metabolism and regulation of seed dormancy. OsNAC2 highly expressed during seed development and germination, and overexpression of OsNAC2 strengthened seed dormancy and suppressed germination. Moreover, exogenous phytohormone treatment showed that OsNAC2 acted upstream of GA signaling and downstream of ABA signaling. Additionally, overexpression of OsNAC2 inhibited ABA degradation and increased ABA content during early germination. Further molecular analysis revealed that OsNAC2 directly bound to the ABA metabolism genes promoter and inhibits their transcription in rice protoplasts. These finding could help us explain the genetic regulation mechanism of ABA metabolism during dormancy release and germination in rice.
•OsNAC2 exhibits high expression levels in ungerminated rice seed embryos, followed by a rapid decline during germination.•Overexpressing OsNAC2 inhibits ABA degradation, maintaining elevated ABA during dormancy release.•OsNAC2 orchestrates hormone responses, including GA, ABA and JA pathways.•OsNAC2 directly binds to the promoters of ABA metabolism genes, thereby exerting transcriptional repression in rice.
SUMMARY
Poor grain filling of inferior spikelets is becoming a severe problem in some super rice varieties with large panicles. Moderate soil drying (MD) after pollination has been proven to be a ...practical strategy to promote grain filling. However, the molecular mechanisms underlying this phenomenon remain largely unexplored. Here, transcriptomic analysis of the most active grain filling stage revealed that both starch metabolism and phytohormone signaling were significantly promoted by MD treatment, accompanied by increased enzyme activities of starch synthesis and elevated abscisic acid (ABA) and indole‐3‐acetic acid (IAA) content in the inferior spikelet. Moreover, the IAA biosynthesis genes OsYUC11 and OsTAR2 were upregulated, while OsIAA29 and OsIAA24, which encode two repressors of auxin signaling, were downregulated by MD, implying a regulation of both IAA biosynthesis and auxin signal transduction in the inferior spikelet by MD. A notable improvement in grain filling of the inferior spikelet was found in the aba8ox2 mutant, which is mutated in an ABA catabolism gene. In contrast, overexpression of OsABA8ox2 significantly reduced grain filling. Interestingly, not only the IAA content, but also the expression of IAA biosynthesis and auxin‐responsive genes displayed a similar trend to that in the inferior spikelet under MD. In addition, several OsTPP genes were downregulated in the inferior spikelets of both MD/ABA‐treated wild‐type plants and the aba8ox2 mutant, resulting in lower trehalose content and higher levels of ‐6‐phosphate (T6P), thereby increasing the expression of OsTAR2, a target of T6P. Taken together, our results suggest that the synergistic interaction of ABA‐mediated accumulation of IAA promotes grain filling of inferior spikelets under MD.
Significance Statement
Post‐anthesis moderate soil drying can increase ABA content in inferior spikelets, which will then activate IAA biosynthesis and IAA signaling. Together, both elevated ABA and IAA play a key role in promoting grain filling of inferior spikelets.
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