In order to understand the salt-tolerance mechanism of alkali grass (Puccinellia tenuiflora) compared with wheat (Triticum aestivum L.), K+ and Na+ in roots and shoots in response to salt treatments ...were examined with ion element analysis and X-ray microanalysis. Both the rapid K+ and Na+ influx in response to different NaCl and KCl treatments, and the accumulation of K+ and Na+ as the plants acclimated to long-term stress were studied in culture- solution experiments. A higher K+ uptake under normal and saline conditions was evident in alkali grass compared with that in wheat, and electrophysiological analyses indicated that the different uptake probably resulted from the higher K+/Na+ selectivity of the plasma membrane. When external K+ was high, K+ uptake and transport from roots to shoots were inhibited by exogenous Cs+, while TEA (tetraethylammonium) only inhibited K+ transport from the root to the shoot. K+ uptake was not influenced by Cs+ when plants were K+ starved. It was shown by X-ray microanalysis that high K+ and low Na+ existed in the endodermal cells of alkali grass roots, suggesting this to be the tissue where Cs+ inhibition occurs. These results suggest that the K+/Na+ selectivity of potassium channels and the existence of an apoplastic barrier, the Casparian bands of the endodermis, lead to the lateral gradient of K+ and Na+ across root tissue, resulting not only in high levels of K+ in the shoot but also a large Na+ gradient between the root and the shoot.
Owing to diverse abiotic stresses and global climate deterioration, the agricultural production worldwide is suffering serious losses. Breeding stress-resilient crops with higher quality and yield ...against multiple environmental stresses via application of transgenic technologies is currently the most promising approach. Deciphering molecular principles and mining stress-associate genes that govern plant responses against abiotic stresses is one of the prerequisites to develop stress-resistant crop varieties. As molecular switches in controlling stress-responsive genes expression, transcription factors (TFs) play crucial roles in regulating various abiotic stress responses. Hence, functional analysis of TFs and their interaction partners during abiotic stresses is crucial to perceive their role in diverse signaling cascades that many researchers have continued to undertake. Here, we review current developments in understanding TFs, with particular emphasis on their functions in orchestrating plant abiotic stress responses. Further, we discuss novel molecular mechanisms of their action under abiotic stress conditions. This will provide valuable information for understanding regulatory mechanisms to engineer stress-tolerant crops.
Salinity and drought are major environmental factors limiting the growth and productivity of alfalfa worldwide as this economically important legume forage is sensitive to these kinds of abiotic ...stress. In this study, transgenic alfalfa lines expressing both tonoplast NXH and H⁺‐PPase genes, ZxNHX and ZxVP1‐1 from the xerophyte Zygophyllum xanthoxylum L., were produced via Agrobacterium tumefaciens‐mediated transformation. Compared with wild‐type (WT) plants, transgenic alfalfa plants co‐expressing ZxNHX and ZxVP1‐1 grew better with greater plant height and dry mass under normal or stress conditions (NaCl or water‐deficit) in the greenhouse. The growth performance of transgenic alfalfa plants was associated with more Na⁺, K⁺ and Ca²⁺ accumulation in leaves and roots, as a result of co‐expression of ZxNHX and ZxVP1‐1. Cation accumulation contributed to maintaining intracellular ions homoeostasis and osmoregulation of plants and thus conferred higher leaf relative water content and greater photosynthesis capacity in transgenic plants compared to WT when subjected to NaCl or water‐deficit stress. Furthermore, the transgenic alfalfa co‐expressing ZxNHX and ZxVP1‐1 also grew faster than WT plants under field conditions, and most importantly, exhibited enhanced photosynthesis capacity by maintaining higher net photosynthetic rate, stomatal conductance, and water‐use efficiency than WT plants. Our results indicate that co‐expression of tonoplast NHX and H⁺‐PPase genes from a xerophyte significantly improved the growth of alfalfa, and enhanced its tolerance to high salinity and drought. This study laid a solid basis for reclaiming and restoring saline and arid marginal lands as well as improving forage yield in northern China.
SUMMARY
Soil salinity is a significant threat to global agriculture. Understanding salt exclusion mechanisms in halophyte species may be instrumental in improving salt tolerance in crops. Puccinellia ...tenuiflora is a typical salt‐excluding halophytic grass often found in potassium‐deprived saline soils. Our previous work showed that P. tenuiflora possesses stronger selectivity for K+ than for Na+; however, the mechanistic basis of this phenomenon remained elusive. Here, P. tenuiflora PutHKT1;5 was cloned and the functions of PutHKT1;5 and PutSOS1 were characterized using heterologous expression systems. Yeast assays showed that PutHKT1;5 possessed Na+ transporting capacity and was highly selective for Na+ over K+. PutSOS1 was located at the plasma membrane and operated as a Na+/K+ exchanger, with much stronger Na+ extrusion capacity than its homolog from Arabidopsis. PutHKT2;1 mediated high‐affinity K+ and Na+ uptake and its expression levels were upregulated by mild salinity and K+ deprivation. Salinity‐induced changes of root PutHKT1;5 and PutHKT1;4 transcript levels matched the expression pattern of root PutSOS1, which was consistent with root Na+ efflux. The transcript levels of root PutHKT2;1 and PutAKT1 were downregulated by salinity. Taken together, these findings demonstrate that the functional activity of PutHKT1;5 and PutSOS1 in P. tenuiflora roots is fine‐tuned under saline conditions as well as by operation of other ion transporters/channel (PutHKT1;4, PutHKT2;1, and PutAKT1). This leads to the coordination of radial Na+ and K+ transport processes, their loading to the xylem, or Na+ retrieval and extrusion under conditions of mild salinity and/or K+ deprivation.
Significance Statement
P. tenuiflora is considered an important model halophyte due to its strong salt tolerance and close genetic relationship with cereals. Here, We aimed to elucidate the coordinated physiological and molecular mechanism for P. tenuiflora adapt to severe salinity and K+ starvation conditions.
Atriplex canescens is a typical C
secretohalophyte with salt bladders on the leaves. Accumulating excessive Na
in tissues and salt bladders, maintaining intracellular K
homeostasis and increasing ...leaf organic solutes are crucial for A. canescens survival in harsh saline environments, and enhanced photosynthetic activity and water balance promote its adaptation to salt. However, the molecular basis for these physiological mechanisms is poorly understood. Four-week-old A. canescens seedlings were treated with 100 mM NaCl for 6 and 24 h, and differentially expressed genes in leaves and roots were identified, respectively, with Illumina sequencing.
In A. canescens treated with 100 mM NaCl, the transcripts of genes encoding transporters/channels for important nutrient elements, which affect growth under salinity, significantly increased, and genes involved in exclusion, uptake and vacuolar compartmentalization of Na
in leaves might play vital roles in Na
accumulation in salt bladders. Moreover, NaCl treatment upregulated the transcripts of key genes related to leaf organic osmolytes synthesis, which are conducive to osmotic adjustment. Correspondingly, aquaporin-encoding genes in leaves showed increased transcripts under NaCl treatment, which might facilitate water balance maintenance of A. canescens seedlings in a low water potential condition. Additionally, the transcripts of many genes involved in photosynthetic electron transport and the C
pathway was rapidly induced, while other genes related to chlorophyll biosynthesis, electron transport and C
carbon fixation were later upregulated by 100 mM NaCl.
We identified many important candidate genes involved in the primary physiological mechanisms of A. canescens salt tolerance. This study provides excellent gene resources for genetic improvement of salt tolerance of important crops and forages.
HKT1 and SOS1 are two key Na⁺ transporters that modulate salt tolerance in plants. Although much is known about the respective functions of HKT1 and SOS1 under salt conditions, few studies have ...examined the effects of
and
mutations on the expression of other important Na⁺ and K⁺ transporter genes. This study investigated the physiological parameters and expression profiles of
,
,
,
,
,
, and
in wild-type (WT) and
and
mutants of
under 25 mM NaCl. We found that
mutation induced a significant decrease in transcripts of
(by 56⁻62% at 6⁻24 h),
(by 36⁻78% at 6⁻24 h), and
(by 31⁻53% at 6⁻24 h) in the roots compared with WT. This led to an increase in Na⁺ accumulation in the roots, a decrease in K⁺ uptake and transportation, and finally resulted in suppression of plant growth.
loss induced a 39⁻76% (6⁻24 h) decrease and a 27⁻32% (6⁻24 h) increase in transcripts of
and
, respectively, in the roots compared with WT. At the same time, 25 mM NaCl decreased the net selective transport capacity for K⁺ over Na⁺ by 92% in the
roots compared with the WT roots. Consequently, Na⁺ was loaded into the xylem and delivered to the shoots, whereas K⁺ transport was restricted. The results indicate that AtHKT1;1 and AtSOS1 not only mediate Na⁺ transport but also control ion uptake and the spatial distribution of Na⁺ and K⁺ by cooperatively regulating the expression levels of relevant Na⁺ and K⁺ transporter genes, ultimately regulating plant growth under salt stress.
The negative impact of soil salinity on agricultural yields is significant. For agricultural plants, sensitivity to salinity is commonly (but not exclusively) due to the abundance of Na+ in the soil ...as excess Na+ is toxic to plants. We consider reducing Na+ uptake to be the key, as well as the most efficient approach, to control Na+ accumulation in crop plants and hence to improve their salt resistance. Understanding the mechanism of Na+ uptake by the roots of higher plants is crucial for manipulating salt resistance. hence, the aim of this review is to highlight and discuss recent advances in our understanding of the mechanisms of Na+ uptake by plant roots at both physiological and molecular levels. We conclude that continued efforts to investigate the mechanisms of root Na+ uptake in higher plants are necessary, especially that of low-affinity Na+ uptake, as it is the means by which sodium enters into plants growing in saline soils.
s (
s) comprise the largest family of early auxin response genes. Some SAURs have been reported to play important roles in plant growth and development, but their functional relationships with auxin ...signaling remain unestablished. Here, we report Arabidopsis (
)
acts downstream of the auxin response factors ARF6,8 and ARF7,19 to regulate auxin signaling-mediated lateral root (LR) and adventitious root (AR) formation. The loss-of-function mutant
exhibits fewer LRs and ARs. By contrast, plants overexpressing
exhibit more LRs and ARs. We find that the
promoter contains four tandem auxin-responsive elements, which are directly bound by ARF6 and ARF7 and are essential for
expression. LR and AR impairment in
and
mutants is partially reduced by ectopic expression of
Additionally, we demonstrate that the ARF6,7-upregulated SAUR15 promotes LR and AR development using two mechanisms. On the one hand, SAUR15 interacts with PP2C-D subfamily type 2C protein phosphatases to inhibit their activities, thereby stimulating plasma membrane H
-ATPases, which drives cell expansion and facilitates LR and AR formation. On the other hand, SAUR15 promotes auxin accumulation, potentially by inducing the expression of auxin biosynthesis genes. A resulting increase in free auxin concentration likely triggers LR and AR formation, forming a feedback loop. Our study provides insights and a better understanding of how SAURs function at the molecular level in regulating auxin-mediated LR and AR development.
Summary
The inward‐rectifying K+ channel AKT1 constitutes an important pathway for K+ acquisition in plant roots. In glycophytes, excessive accumulation of Na+ is accompanied by K+ deficiency under ...salt stress. However, in the succulent xerophyte Zygophyllum xanthoxylum, which exhibits excellent adaptability to adverse environments, K+ concentration remains at a relatively constant level despite increased levels of Na+ under salinity and drought conditions. In this study, the contribution of ZxAKT1 to maintaining K+ and Na+ homeostasis in Z. xanthoxylum was investigated. Expression of ZxAKT1 rescued the K+‐uptake‐defective phenotype of yeast strain CY162, suppressed the salt‐sensitive phenotype of yeast strain G19, and complemented the low‐K+‐sensitive phenotype of Arabidopsis akt1 mutant, indicating that ZxAKT1 functions as an inward‐rectifying K+ channel. ZxAKT1 was predominantly expressed in roots, and was induced under high concentrations of either KCl or NaCl. By using RNA interference technique, we found that ZxAKT1‐silenced plants exhibited stunted growth compared to wild‐type Z. xanthoxylum. Further experiments showed that ZxAKT1‐silenced plants exhibited a significant decline in net uptake of K+ and Na+, resulting in decreased concentrations of K+ and Na+, as compared to wild‐type Z. xanthoxylum grown under 50 mm NaCl. Compared with wild‐type, the expression levels of genes encoding several transporters/channels related to K+/Na+ homeostasis, including ZxSKOR, ZxNHX, ZxSOS1 and ZxHKT1;1, were reduced in various tissues of a ZxAKT1‐silenced line. These findings suggest that ZxAKT1 not only plays a crucial role in K+ uptake but also functions in modulating Na+ uptake and transport systems in Z. xanthoxylum, thereby affecting its normal growth.
Significance Statement
Succulent plants can better adapt to drought and salinity. Here we show that an inward‐rectifying potassium channel (ZxAKT1) contributes to this adaptation in Z. xanthoxylum, as unlike in glycophytes, where excessive accumulation of Na+ is accompanied by K+ deficiency under salt stress, in succulents K+ was maintained at a relatively constant level, despite increased Na+. Thus ZxAKT1 not only plays a crucial role in K+ uptake but also functions in modulating Na+ uptake and transport systems.
Background
Under saline conditions,
Suaeda salsa
, as a typical halophyte, accumulates large amounts of Na
+
in its leaves during optimal growth. Key transporters involved in Na
+
accumulation in ...plants are HKT-type protein, the plasma membrane Na
+
/H
+
transporter SOS1, and the tonoplast Na
+
/H
+
antiporter NHX1. In this study, the function of SsHKT1;1 and its coordinate expression with SsSOS1 and SsNHX1 to regulate Na
+
homeostasis in
S. salsa
was investigated.
Results
We showed, by yeast complementation assays, that
SsHKT1;1
encoded a Na
+
-selective transporter, which located to the plasma membrane and was preferentially expressed within the stele, and was particularly abundant in xylem parenchyma and pericycle cells. When compared with a treatment of 25 mM NaCl, 150 mM NaCl greatly decreased the transcripts of
SsHKT1;1
, but maintained a relatively constant level of the expression of
SsSOS1
in roots. Consequently, the synergistic effect of SsHKT1;1 and SsSOS1 would result in greater Na
+
loading into the xylem under 150 mM NaCl than 25 mM NaCl. In leaves, 150 mM NaCl up-regulated the abundance of
SsNHX1
compared with levels in 25 mM NaCl. This enabled the permanent sequestering of Na
+
into leaf vacuoles.
Conclusions
Overall, SsHKT1;1 functioned in reducing Na
+
retrieval from the root xylem, and played an important role in coordinating with SsSOS1 and SsNHX1 to maintain Na
+
accumulation in
S. salsa
under saline conditions.
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