Rice 7-Hydroxymethyl Chlorophyll a Reductase Is Involved in the Promotion of Chlorophyll Degradation and Modulates Cell Death Signaling

The SUMO-conjugating enzyme OsSCE1a from wild rice regulates the functional stay-green trait in rice

The functional stay-green trait is a major goal of rice breeding. Here, we cloned OsSCE1a encoding SUMO-conjugating enzyme from Yuanjiang common wild rice, which simultaneously regulates the functional stay-green trait and growth duration. Low expression or knocking out OsSCE1a corresponded to increased chlorophyll content, photosynthetic competence, N use efficiency and a shortened growth period without affecting yield. A natural MITE-transposon insertion/deletion in the OsSCE1a promoter is the functional variation that regulates these traits. OsSCE1a was selected during evolution and shows significant variation between indica and japonica rice. OsNAC2 interacts with the MITE to enhance OsSCE1a expression. Genetic manipulation of OsSCE1a revealed its potential for rice improvement. OsSCE1a-mediated SUMOylation of OsGS2 suppresses GS (involved in N assimilation) enzyme activity. OsSCE1a also regulates growth duration by SUMOylating the transcription factor such as OsGBP1, which regulates the expression of the key heading gene Ghd7. Our findings shed light on the role of SUMOylation in crops and provide a strategy for increasing agricultural productivity.

Comparative transcriptome and metabolomic analysis reveal key genes and mechanisms responsible for the dark-green leaf color of a strawberry mutant

Photosynthesis is a source of energy for various types of plant life activities and is essential for plant growth and development. Consequently, the study of photosynthetic mechanisms has been a hot spot. Leaf color mutants has always been ideal materials for exploring the mechanisms of chlorophyll metabolism and photosynthesis. In this study, we identified a leaf color mutant of 'Benihoppe' strawberry in the field, which exhibited a darker green leaf color compared with the wild type. The content of total chlorophyll and carotenoid in the mutant leaves was elevated by 7.44-20.23% and 8.9-21.92%, respectively, compared with that of the wild type. Additionally, net photosynthetic rate in the mutant increased by 20.13%. Further transcriptome analysis showed that significant upregulation of genes such as GLK1, PPR, and MORF9 in the mutant leaves, which promoted chloroplast development. The expression levels of UROD, PPOC, PORA, CHLG, and CPOX were significantly upregulated during chlorophyll synthesis, while the expression levels of HCAR and CYP89A9 were significantly downregulated during chlorophyll degradation, thus leading to the accumulation of chlorophyll in mutant leaves. The upregulation of gene expression levels such as PetM, AtpD, PGK, and RPI4 during photosynthesis promoted multiple stages of light and dark reaction, thereby enhancing the photosynthetic capacity of the mutant. And the changes in metabolites such as monogalactosyl monoacylglycerol (MGMG), glucuronosyldiacylglycerol (GlcADG), raffinose, etc. also indicate that the mutant has metabolic differences in chloroplast composition and photosynthesis compared to 'Benihoppe'. The above results not only deepen our understanding of the mechanism behind the dark-green leaf color in strawberry mutants but also provide potential genetic resources for cultivating strawberry varieties with enhanced photosynthetic capacity.

Identification, genomic localization, and functional validation of salt-stress-related lncRNAs in Indian Mustard (Brassica juncea L.)

Indian Mustard (Brassica juncea L.) is a globally cultivated winter oilseed crop of the rapeseed-mustard group. It is predominantly grown in the semi-arid northwest agroclimatic zone of India, characterized by high soil salinity. Enhancing tolerance to salt stress in B. juncea is therefore crucial for sustaining its production in this region. Long non-coding RNAs (lncRNAs) play critical roles in coordinating gene expression under various abiotic stresses, including salt stress, but their involvement in the salt stress response in B. juncea remains largely unknown. In this study, we conducted RNA-seq analysis on control, salt-stressed, and salt-shocked young leaves of the salt-tolerant B. juncea cv CS-52. We identified a total of 3,602 differentially expressed transcripts between stress versus control and shock versus control samples. Among these, 61 were identified as potential lncRNAs, with 21 specific to salt stress and 40 specific to salt shock. Of the 21 lncRNAs specific to salt stress, 15 were upregulated and six were downregulated, while all 40 lncRNAs unique to salt shock were downregulated. Chromosomal distribution analysis of the lncRNAs revealed their uneven placement across 18 chromosomes in B. juncea. RNA-RNA interaction analysis between salt stress-upregulated lncRNAs and salt stress-related miRNAs identified 26 interactions between 10 lncRNAs and 23 miRNAs and predicted 13 interactions between six miRNAs and 13 mRNAs. Finally, six lncRNA-miRNA-mRNA interaction networks were established, involving five lncRNAs, 13 miRNAs, and 23 mRNAs. RT-qPCR analysis revealed the upregulation of four out of five lncRNAs, along with their target mRNAs, supporting their involvement in the salt stress response in B. juncea.

OsNAC103, a NAC Transcription Factor, Positively Regulates Leaf Senescence and Plant Architecture in Rice

Leaf senescence, the last stage of leaf development, is essential for crop yield by promoting nutrition relocation from senescence leaves to new leaves and seeds. NAC (NAM/ATAF1/ATAF2/CUC2) proteins, one of the plant-specific transcription factors, widely distribute in plants and play important roles in plant growth and development. Here, we identified a new NAC member OsNAC103 and found that it plays critical roles in leaf senescence and plant architecture in rice. OsNAC103 mRNA levels were dramatically induced by leaf senescence as well as different phytohormones such as ABA, MeJA and ACC and abiotic stresses including dark, drought and high salinity. OsNAC103 acts as a transcription factor with nuclear localization signals at the N terminal and a transcriptional activation signal at the C terminal. Overexpression of OsNAC103 promoted leaf senescence while osnac103 mutants delayed leaf senescence under natural condition and dark-induced condition, meanwhile, senescence-associated genes (SAGs) were up-regulated in OsNAC103 overexpression (OsNAC103-OE) lines, indicating that OsNAC103 positively regulates leaf senescence in rice. Moreover, OsNAC103-OE lines exhibited loose plant architecture with larger tiller angles while tiller angles of osnac103 mutants decreased during the vegetative and reproductive growth stages due to the response of shoot gravitropism, suggesting that OsNAC103 can regulate the plant architecture in rice. Taken together, our results reveal that OsNAC103 plays crucial roles in the regulation of leaf senescence and plant architecture in rice.

Rice Basic Helix-Loop-Helix 079 (OsbHLH079) Delays Leaf Senescence by Attenuating ABA Signaling

Leaf senescence represents the final phase of leaf development and is characterized by a highly organized degenerative process involving the active translocation of nutrients from senescing leaves to growing tissues or storage organs. To date, a large number of senescence-associated transcription factors (sen-TFs) have been identified that regulate the initiation and progression of leaf senescence. Many of these TFs, including NAC (NAM/ATAF1/2/CUC2), WRKY, and MYB TFs, have been implicated in modulating the expression of downstream senescence-associated genes (SAGs) and chlorophyll degradation genes (CDGs) under the control of phytohormones. However, the involvement of basic helix-loop-helix (bHLH) TFs in leaf senescence has been less investigated. Here, we show that OsbHLH079 delays both natural senescence and dark-induced senescence: Overexpression of OsbHLH079 led to a stay-green phenotype, whereas osbhlh079 knockout mutation displayed accelerated leaf senescence. Similar to other sen-TFs, OsbHLH079 showed a gradual escalation in expression as leaves underwent senescence. During this process, the mRNA levels of SAGs and CDGs remained relatively low in OsbHLH079 overexpressors, but increased sharply in osbhlh079 mutants, suggesting that OsbHLH079 negatively regulates the transcription of SAGs and CDGs under senescence conditions. Additionally, we found that OsbHLH079 delays ABA-induced senescence. Subsequent RT-qPCR and dual-luciferase reporter assays revealed that OsbHLH079 downregulates the expression of ABA signaling genes, such as OsABF2, OsABF4, OsABI5, and OsNAP. Taken together, these results demonstrate that OsbHLH079 functions in delaying leaf yellowing by attenuating the ABA responses.

Mapping the gene of a maize leaf senescence mutant and understanding the senescence pathways by expression analysis

KEY MESSAGES

Narrowing down to a single putative target gene behind a leaf senescence mutant and constructing the regulation network by proteomic method. Leaf senescence mutant is an important resource for exploring molecular mechanism of aging. To dig for potential modulation networks during maize leaf aging process, we delimited the gene responsible for a premature leaf senescence mutant els5 to a 1.1 Mb interval in the B73 reference genome using a BC1F1 population with 40,000 plants, and analyzed the leaf proteomics of the mutant and its near-isogenic wild type line. A total of 1355 differentially accumulated proteins (DAP) were mainly enriched in regulation pathways such as "photosynthesis", "ribosome", and "porphyrin and chlorophyll metabolism" by the KEGG pathway analysis. The interaction networks constructed by incorporation of transcriptome data showed that ZmELS5 likely repaired several key factors in the photosynthesis system. The putative candidate proteins for els5 were proposed based on DAPs in the fined QTL mapping interval. These results provide fundamental basis for cloning and functional research of the els5 gene, and new insights into the molecular mechanism of leaf senescence in maize.

Genome-Wide Identification and Expression Analysis of Senescence-Associated Genes in Grapevine (Vitis vinifera L.) Reveal Their Potential Functions in Leaf Senescence Order

Natural leaf senescence is an acclimation strategy that enables plants to reallocate nutrients. In the present study, interestingly, we found that the basal mature leaves of grapevine primary shoots (P) exhibited the earliest senescence, followed by the apical young leaves of secondary shoots (ST), and then the basal mature leaves of secondary shoots (S). The Chl level decreased with the extent of leaf senescence. According to the genome-wide identification and expression analysis, sixteen senescence-associated genes (SAGs) involved in Chl breakdown were identified in the grapevine genome. Their expression patterns showed that the transcript changes in VvSGR, VvPPH2, and VvFtsH6-2 corresponded to the changes in Chl content among P, S, and ST. The changes in the transcription of VvNYC1, VvSGR, VvPAO1, VvPAO2, VvPAO4, VvPPH1, VvPPH3, and VvFtsH6-1 only contributed to low Chl levels in P. The cis-element analysis indicated that these SAGs possessed several light- and hormone-responsive elements in their promoters. Among them, ABA-responsive elements were found in twelve of the sixteen promoters of SAGs. Correspondingly, ABA-signaling components presented various changes in transcription among P, S, and ST. The transcription changes in VvbZIP45 and VvSnRK2.1 were similar to those in VvSGR, VvPPH2, and VvFtsH6-2. The other nine ABA-signaling components, which included VvRCAR2, VvRCAR4, VvRCAR6, VvRCAR7, VvRCAR2, VvPP2C4, VvPP2C9, VvbZIP25, and VvSnRK2.3, were highly expressed in P but there was no difference between S and ST, with similar expression patterns for VvNYC1, VvSGR, VvPAO1, VvPAO2, VvPAO4, VvPPH1, VvPPH3, and VvFtsH6-1. These results suggested that the senescence of P and ST could be regulated by different members of Chl breakdown-related SAGs and ABA-signaling components. These findings provide us with important candidate genes to further study the regulation mechanism of leaf senescence order in grapevine.

Overexpression of 7-hydroxymethyl Chlorophyll a Reductase from Cucumber in Tobacco Accelerates Dark-Induced Chlorophyll Degradation

7-hydroxymethyl chlorophyll (Chl) a reductase (HCAR) plays critical roles in the Chl cycle and degradation during leaf senescence, however, its function in horticultural crops remains unknown. Here, we identified an HCAR gene (CsHCAR) from cucumber (Cucumis sativus L.) and investigated its roles in response to dark-induced Chl degradation. CsHCAR encoded 459 amino acids, which were orthologous to Arabidopsis HCAR, had the conserved domains, and localized in the chloroplast. Gene expression analysis showed that CsHCAR expression was the highest in senescent leaves and was responsive to different stresses and phytohormone treatments. Overexpression of CsHCAR in tobacco accelerated dark-induced Chl degradation through enhancing the expression of Chl catabolic genes. After 10 d of darkness treatment, the biomass of CsHCAR overexpression plants was reduced. Furthermore, the value of net photosynthetic rate, maximum quantum yield of photosystem II, and effective quantum yield of photosystem II in CsHCAR overexpression plants was significantly reduced in comparison to that in wild-type (WT) plants. The photosynthetic protein content, including Lhcb1, Lhcb2, Lhcb4, RbcS, and RbcL in CsHCAR overexpression plants exhibited a lower level as compared to that observed in WT plants. In addition, the expression of genes encoding these proteins in CsHCAR overexpression plants was significantly lower than that in WT plants. Moreover, CsHCAR overexpression plants inhibited the dark-induced accumulation of reactive oxygen species (ROS). These results indicate that CsHCAR affects the stability of photosynthetic proteins in chloroplasts, positively regulates Chl degradation, and plays an important role in maintaining ROS homeostasis in leaves.

A Novel Allele Encoding 7-Hydroxymethyl Chlorophyll a Reductase Confers Bacterial Blight Resistance in Rice

Rice spotted leaf mutants are helpful to investigate programmed cell death (PCD) and defense response pathways in plants. Using a map-based cloning strategy, we characterized novel rice spotted leaf mutation spl^HM143 that encodes a 7-hydroxymethyl chlorophyll a reductase (OsHCAR). The wild-type (WT) allele could rescue the mutant phenotype, as evidenced by complementation analysis. OsHCAR was constitutively expressed at all rice tissues tested and its expression products localized to chloroplasts. The mutant exhibited PCD and leaf senescence with increased H₂O₂ (hydrogen peroxide) accumulation, increased of ROS (reactive oxygen species) scavenging enzymes activities and TUNEL (terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling) -positive nuclei, upregulation of PCD related genes, decreased chlorophyll (Chl) contents, downregulation of photosynthesis-related genes, and upregulation of senescence-associated genes. Besides, the mutant exhibited enhanced bacterial blight resistance with significant upregulation of defense response genes. Knockout lines of OsHCAR exhibited spotted leaf phenotype, cell death, leaf senescence, and showed increased resistance to the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) coupled with upregulation of five pathogenesis-related marker genes. The overexpression of OsHCAR resulted in increased susceptibility to Xoo with decreased expression of pathogenesis-related marker genes. Altogether, our findings revealed that OsHCAR is involved in regulating cell death and defense response against bacterial blight pathogen in rice.

Current Understanding of Leaf Senescence in Rice

Leaf senescence, which is the last developmental phase of plant growth, is controlled by multiple genetic and environmental factors. Leaf yellowing is a visual indicator of senescence due to the loss of the green pigment chlorophyll. During senescence, the methodical disassembly of macromolecules occurs, facilitating nutrient recycling and translocation from the sink to the source organs, which is critical for plant fitness and productivity. Leaf senescence is a complex and tightly regulated process, with coordinated actions of multiple pathways, responding to a sophisticated integration of leaf age and various environmental signals. Many studies have been carried out to understand the leaf senescence-associated molecular mechanisms including the chlorophyll breakdown, phytohormonal and transcriptional regulation, interaction with environmental signals, and associated metabolic changes. The metabolic reprogramming and nutrient recycling occurring during leaf senescence highlight the fundamental role of this developmental stage for the nutrient economy at the whole plant level. The strong impact of the senescence-associated nutrient remobilization on cereal productivity and grain quality is of interest in many breeding programs. This review summarizes our current knowledge in rice on (i) the actors of chlorophyll degradation, (ii) the identification of stay-green genotypes, (iii) the identification of transcription factors involved in the regulation of leaf senescence, (iv) the roles of leaf-senescence-associated nitrogen enzymes on plant performance, and (v) stress-induced senescence. Compiling the different advances obtained on rice leaf senescence will provide a framework for future rice breeding strategies to improve grain yield.

Cold acclimation can specifically inhibit chlorophyll biosynthesis in young leaves of Pakchoi

BACKGROUND

Leaf color is an important trait in breeding of leafy vegetables. Y-05, a pakchoi (Brassica rapa ssp. chinensis) cultivar, displays yellow inner (YIN) and green outer leaves (GOU) after cold acclimation. However, the mechanism of this special phenotype remains elusive.

RESULTS

We assumed that the yellow leaf phenotype of Y-05 maybe caused by low chlorophyll content. Pigments measurements and transmission electron microscopy (TEM) analysis showed that the yellow phenotype is closely related with decreased chlorophyll content and undeveloped thylakoids in chloroplast. Transcriptomes and metabolomes sequencing were next performed on YIN and GOU. The transcriptomes data showed that 4887 differentially expressed genes (DEGs) between the YIN and GOU leaves were mostly enriched in the chloroplast- and chlorophyll-related categories, indicating that the chlorophyll biosynthesis is mainly affected during cold acclimation. Together with metabolomes data, the inhibition of chlorophyll biosynthesis is contributed by blocked 5-aminolevulinic acid (ALA) synthesis in yellow inner leaves, which is further verified by complementary and inhibitory experiments of ALA. Furthermore, we found that the blocked ALA is closely associated with increased BrFLU expression, which is indirectly altered by cold acclimation. In BrFLU-silenced pakchoi Y-05, cold-acclimated leaves still showed green phenotype and higher chlorophyll content compared with control, meaning silencing of BrFLU can rescue the leaf yellowing induced by cold acclimation.

CONCLUSIONS

Our findings suggested that cold acclimation can indirectly promote the expression of BrFLU in inner leaves of Y-05 to block ALA synthesis, resulting in decreased chlorophyll content and leaf yellowing. This study revealed the underlying mechanisms of leaves color change in cold-acclimated Y-05.

Genome-wide identification and characterization of long non-coding RNAs involved in flag leaf senescence of rice

KEY MESSAGE

This study showed the systematic identification of long non-coding RNAs (lncRNAs) involving in flag leaf senescence of rice, providing the possible lncRNA-mRNA regulatory relationships and lncRNA-miRNA-mRNA ceRNA networks during leaf senescence. LncRNAs have been reported to play crucial roles in diverse biological processes. However, no systematic identification of lncRNAs associated with leaf senescence in plants has been studied. In this study, a genome-wide high throughput sequencing analysis was performed using rice flag leaves developing from normal to senescence. A total of 3953 lncRNAs and 38757 mRNAs were identified, of which 343 lncRNAs and 9412 mRNAs were differentially expressed. Through weighted gene co-expression network analysis (WGCNA), 22 continuously down-expressed lncRNAs targeting 812 co-expressed mRNAs and 48 continuously up-expressed lncRNAs targeting 1209 co-expressed mRNAs were considered to be significantly associated with flag leaf senescence. Gene Ontology results suggested that the senescence-associated lncRNAs targeted mRNAs involving in many biological processes, including transcription, hormone response, oxidation-reduction process and substance metabolism. Additionally, 43 senescence-associated lncRNAs were predicted to target 111 co-expressed transcription factors. Interestingly, 8 down-expressed lncRNAs and 29 up-expressed lncRNAs were found to separately target 12 and 20 well-studied senescence-associated genes (SAGs). Furthermore, analysis on the competing endogenous RNA (CeRNA) network revealed that 6 down-expressed lncRNAs possibly regulated 51 co-expressed mRNAs through 15 miRNAs, and 14 up-expressed lncRNAs possibly regulated 117 co-expressed mRNAs through 21 miRNAs. Importantly, by expression validation, a conserved miR164-NAC regulatory pathway was found to be possibly involved in leaf senescence, where lncRNA MSTRG.62092.1 may serve as a ceRNA binding with miR164a and miR164e to regulate three transcription factors. And two key lncRNAs MSTRG.31014.21 and MSTRG.31014.36 also could regulate the abscisic-acid biosynthetic gene BGIOSGA025169 (OsNCED4) and BGIOSGA016313 (NAC family) through osa-miR5809. The possible regulation networks of lncRNAs involving in leaf senescence were discussed, and several candidate lncRNAs were recommended for prior transgenic analysis. These findings will extend the understanding on the regulatory roles of lncRNAs in leaf senescence, and lay a foundation for functional research on candidate lncRNAs.

Light-Mediated Regulation of Leaf Senescence

Light is the primary regulator of various biological processes during the plant life cycle. Although plants utilize photosynthetically active radiation to generate chemical energy, they possess several photoreceptors that perceive light of specific wavelengths and then induce wavelength-specific responses. Light is also one of the key determinants of the initiation of leaf senescence, the last stage of leaf development. As the leaf photosynthetic activity decreases during the senescence phase, chloroplasts generate a variety of light-mediated retrograde signals to alter the expression of nuclear genes. On the other hand, phytochrome B (phyB)-mediated red-light signaling inhibits the initiation of leaf senescence by repressing the phytochrome interacting factor (PIF)-mediated transcriptional regulatory network involved in leaf senescence. In recent years, significant progress has been made in the field of leaf senescence to elucidate the role of light in the regulation of nuclear gene expression at the molecular level during the senescence phase. This review presents a summary of the current knowledge of the molecular mechanisms underlying light-mediated regulation of leaf senescence.

HCAR Is a Limitation Factor for Chlorophyll Cycle and Chlorophyll b Degradation in Chlorophyll-b-Overproducing Plants

The chlorophyll (Chl) cycle is the metabolic pathway for Chl a and Chl b inter-conversion. In this pathway, Chl b is synthesized from Chl a by the catalyzing action of chlorophyllide a oxygenase (CAO). In contrast, Chl b is firstly reduced to produce 7-hydroxymethyl Chl (HMChl) a, which is catalyzed by two isozymes of Chl b reductase (CBR), non-yellow coloring 1 (NYC1) and NYC1-like (NOL). Subsequently, HMChl a is reduced to Chl a by HMChl a reductase (HCAR). CAO plays a pivotal role in Chl a/b ratio regulation and plants over-accumulate Chl b in CAO-overexpressing plants. NYC1 is more accumulated in Chl-b-overproducing plants, while HCAR is not changed. To investigate the role of HCAR in Chl cycle regulation, the Chl metabolites of Chl-b-overproducing plants were analyzed. The results showed that HMChl a accumulated in these plants, and it decreased and the Chl a/b ratio increased by overexpressing HCAR, implying HCAR is insufficient for Chl cycle in Chl-b-overproducing plants. Furthermore, during dark-induced senescence, the non-programmed cell death symptoms (leaves dehydrated with green color retained) of Chl-b-overproducing plants were obviously alleviated, and the content of HM pheophorbide (HMPheide) a and Pheide b were sharply decreased by overexpressing HCAR. These results imply that HCAR is also insufficient for Chl degradation in Chl-b-overproducing plants during senescence, thus causing the accumulation of Chl metabolites and non-programmed cell death of leaves. With these results taken together, we conclude that HCAR is not well regulated and it is a limiting factor for Chl cycle and Chl b degradation in Chl-b-overproducing plants.

A Synthetic Cytokinin Improves Photosynthesis in Rice under Drought Stress by Modulating the Abundance of Proteins Related to Stomatal Conductance, Chlorophyll Contents, and Rubisco Activity

Drought susceptible rice cultivar PTT1 (Pathumthani1) was treated with drought (-72 kPa) and CPPU (N-2-(chloro-4-pyridyl)-N-phenyl urea) @ 5 mg/L at tillering and grain-filling stages. Plants were tested for the effect of synthetic cytokinin on the parameters influencing the process of photosynthesis. Exogenous spray of CPPU improved the stomatal conductance of rice leaves, which was severely reduced by drought. The abundance intensities of proteins, associated with the stomatal conductance (ZEP, NCED4, PYL9, PYL10, ABI5, SnRK4, Phot1, and Phot2), were also in agreement with the positive impact of CPPU on the stomatal conductance under drought stress. Among the photosynthetic pigments, Chl b contents were significantly reduced by drought stress, whereas CPPU treated plants retained the normal contents of Chl b under drought stress. Subsequently, we examined the abundance intensities of chlorophyll synthase and HCR proteins, implicated in the biosynthesis of chlorophyll pigments and the conversion of Chl b to Chl a, respectively. The results indicated a drought-mediated suppression of chlorophyll synthase. However, CPPU treated plants retained normal levels of chlorophyll synthase under drought stress. In addition, drought stress induced HCR proteins, which might be the cause for reduced Chl b contents in drought stressed plants. Further, CPPU treatment helped the plants sustain photosynthesis at a normal rate under drought stress, which was comparable with well-watered plants. The results were further confirmed by examining the abundance intensities of two key proteins, RAF1 and Rubisco activase, implicated in the assembly and activation of Rubisco, respectively. CPPU treatment reversed the drought mediated suppression of these proteins at both of the growth stages of rice under drought stress. Based on the results, it can be suggested that synthetic cytokinins help the plants sustain photosynthesis at a normal rate under drought stress by positively influencing the determinants of photosynthesis at a molecular level.

Physiological Analysis and Proteome Quantification of Alligator Weed Stems in Response to Potassium Deficiency Stress

The macronutrient potassium is essential to plant growth, development and stress response. Alligator weed (Alternanthera philoxeroides) has a high tolerance to potassium deficiency (LK) stress. The stem is the primary organ responsible for transporting molecules from the underground root system to the aboveground parts of the plant. However, proteomic changes in response to LK stress are largely unknown in alligator weed stems. In this study, we investigated the physiological and proteomic changes in alligator weed stems under LK stress. First, the chlorophyll and soluble protein content and SOD and POD activity were significantly altered after 15 days of LK treatment. The quantitative proteomic analysis suggested that a total of 296 proteins were differentially abundant proteins (DAPs). The functional annotation analysis revealed that LK stress elicited complex proteomic alterations that were involved in oxidative phosphorylation, plant-pathogen interactions, glycolysis/gluconeogenesis, sugar metabolism, and transport in stems. The subcellular locations analysis suggested 104 proteins showed chloroplastic localization, 81 proteins showed cytoplasmic localization and 40 showed nuclear localization. The protein–protein interaction analysis revealed that 56 proteins were involved in the interaction network, including 9 proteins involved in the ribosome network and 9 in the oxidative phosphorylation network. Additionally, the expressed changes of 5 DAPs were similar between the proteomic quantification analysis and the PRM-MS analysis, and the expression levels of eight genes that encode DAPs were further verified using an RT-qPCR analysis. These results provide valuable information on the adaptive mechanisms in alligator weed stems under LK stress and facilitate the development of efficient strategies for genetically engineering potassium-tolerant crops.