Plant and Cell Physiology最新文献

We investigated the spatial dynamics of potato (Solanum tuberosum) responses to herbivory and mechanical wounding. We first followed the spatiotemporal response of jasmonic acid (JA) signaling, known to be involved in the response. We generated two potato sensor lines: a JAZ degradation sensor and a downstream multicystatin (MC) transcriptional reporter. Both sensors revealed concentric, locally restricted responses on wounded leaves. Notably, JA-dependent gene expression was absent in cells immediately adjacent to the wound, whereas JAZ degradation spread continuously outward from the wound site. This pattern occurred after both herbivore attack and mechanical injury by the needle. To probe the mechanism, a salicylic acid (SA) reporter showed SA accumulation near the wound. Introducing the MC reporter into SA-depleted NahG plants produced a uniform spread of MC expression, confirming that SA attenuates the JA response in proximal cells. Together, these results show that a locally distinct, spatiotemporal SA-JA crosstalk shapes wound responses in potato, extending principles known from pathogen-plant interactions to herbivory and mechanical damage.

Plant cell wall polysaccharide glycosyltransferases catalyze the transfer of sugars from specific nucleotide sugar donors onto specific acceptor substrates. The mechanisms of how their enzymatic specificity is determined are one of the long-standing questions in plant cell wall biology. In this report, we studied the biochemical functions of Arabidopsis and poplar GT61 glycosyltransferases involved in xylan substitutions and investigated the molecular determinants of their nucleotide sugar donor specificity. Enzymatic activity assays of recombinant proteins of Arabidopsis and poplar GT61 members demonstrated that two of them, AtX2AT1 and PtrX2AT1, exhibited xylan 2-O-arabinosyltransferase activities specifically using UDP-Araf, two other ones, AtXYXT2/3, possessed xylan 2-O-xylosyltransferase activities specifically using UDP-Xyl, and three other ones, PtrXXAT1/2/3, were able to catalyze the transfer of 2-O-Araf and 2-O-Xyl onto xylan using both UDP-Araf and UDP-Xyl. Structural modeling and molecular docking of PtrXXAT1 identified amino acid residues involved in interacting with UDP-Araf and UDP-Xyl at the putative active site and site-directed mutagenesis revealed their critical roles in PtrXXAT1 catalytic activities. Furthermore, structural alignment and reciprocal swapping of UDP-Xyl-interacting residues of PtrXXAT1 with their corresponding residues of AtX2AT1 pinpointed key residues determining their nucleotide sugar donor specificity. Our results indicate that Arabidopsis and poplar GT61 members catalyze 2-O-Araf- and/or 2-O-Xyl substitutions of xylan and that subtle structural differences in their substrate-binding pockets could alter their substrate specificity toward nucleotide sugar donors.

The symbiotic association of legumes with rhizobia results in the formation of new root organs called nodules. However, the lifespan of nodules is limited by the senescence process. Increased proteolytic activity is one of the hallmarks of nodule senescence. In Medicago truncatula, a papain cysteine protease encoding gene, MtCP6, is a marker for the onset of nodule senescence under both developmental and stress-induced pathways. To identify the promoter regions responsible for the senescence-related expression of MtCP6, progressive MtCP6 promoter deletions were generated and fused with the GUS reporter for promoter::GUS activity analysis in transgenic M. truncatula roots. In planta, a minimal promoter sequence of 67 bp was identified as sufficient for specific spatiotemporal transcriptional activation of MtCP6 in nodules. The functionality of this promoter regulatory module, thereafter named 'nodule senescence (NS) promoter regulatory module', was validated by both gain- and loss-of-function approaches in M. truncatula. A yeast-one-hybrid (Y1H) screen identified the AP2/ERF transcription factor ERF091, shown to positively regulate nodulation in Lotus japonicus, as an NS- interacting factor. Further Y1H and Nicotiana transactivation assays demonstrated the specificity of ERF91 to interact with and mediate transcription activation of the NS promoter regulatory motif. This work has uncovered a new senescence-related nodule-specific regulatory region and provides evidence for the likely involvement of a stress-related ERF family member in the regulation of MtCP6, at the onset of nodule senescence.

ABA signaling in stomatal guard cells is crucial for plants to cope with abiotic stress condition. Pyrabactin is a synthetic agonist of ABA that has a selective affinity to limited isoforms of ABA receptors. Here, we investigated the differential utilization of downstream signaling events in guard cell ABA signaling under specific receptor isoforms taking advantage of pyrabactin affinity. Pyrabactin-induced stomatal closure as well as ABA, while it did not inhibit stomatal opening. Plasma membrane inwardly rectifying K+ channel was not regulated by pyrabactin, while H+-ATPase activation was negatively regulated by pyrabactin. Pharmacological and molecular genetic evidence supported that reactive oxygen species production occurred differentially between the closure-inducing and opening-inhibiting signals in guard cells. These findings offer a previously unidentified mechanism for ABA signaling events promoting closure induction and opening inhibition of stomata, which were distinct from each other and governed by different ABA receptor isoforms discriminable by their affinity for pyrabactin.

The noni (Morinda citrifolia) fruit undergoes exclusive postharvest changes in metabolites to counteract spoilage. The second day after harvest is the key time point for noni fruit, which would generate high content of scopoletin after that. According to our previous RNA-seq data, the McACO2 genes encode aminocyclopropane carboxylic acid oxidase, a key enzyme involved in ethylene biosynthesis, were identified to be closely related to the postharvest ripening process of noni fruit. Ethylene is a signaling molecule for scopoletin biosynthesis. To reveal the relationship between McACO2 and scopoletin biosynthesis, here we cloned the McACO2 gene and verified its function through noni genetic transformation. In McACO2-OE lines, McACO2 expression, McACO enzyme activity, and scopoletin content were significantly higher than those of wild type. Conversely, in McACO2-RNAi lines, McACO2 expression, McACO enzyme activity, and scopoletin content were significantly lower than those of wild type. The expression levels of genes enriched in the MAPK signaling, phenylpropanoid biosynthesis, ethylene biosynthesis, and plant hormone signal transduction pathways were altered by McACO2. The McACO2 gene promoter responded to ethylene, and the ethylene-responsive element in -1802 to -1619 bp was negatively regulated by exogenous ethylene, suppressing the expression of downstream McACO2 gene, while the ethylene-responsive element in -659 to -467 bp was positively regulated by exogenous ethylene, promoting the expression of downstream McACO2 gene. In summary, the McACO2 gene plays a critical role in scopoletin biosynthesis regulation by altering ethylene levels and the expression of corresponding genes related to the phenylpropanoid pathway, and improves scopoletin contents in the postharvest noni fruit. Our findings suggest an ethylene-mediated scopoletin biosynthesis pathway involving the McACO2 gene, which provides new insights for maintaining or improving the quality of postharvest noni fruit.

Under natural growth conditions, plants are constantly exposed to changes in light intensity. PROTON GRADIENT REGULATION 5 (PGR5)-dependent photosystem I cyclic electron transport (PSI-CET) is known to be required to protect PSI from photoinhibition during such fluctuating light. Moreover, the Arabidopsis thaliana (Arabidopsis) pgr5 mutant cannot survive under fluctuating light conditions due to severe PSI photoinhibition. Recently, we demonstrated that the thioredoxin (Trx) system also supports PSI photoprotection under fluctuating light conditions. Of the five Trx types in Arabidopsis chloroplasts, the x- and y-type Trxs prevent over-reduction of the PSI acceptor side. In the mutant lacking both types (trx x trx y1y2), strong acceptor-side limitation and PSI photoinhibition occurred. To further clarify the roles of PSI-CET and the Trx system in PSI photoprotection, we analyzed multiple mutants. In the pgr5-5 trx x trx y1y2 quadruple mutant, the PSI acceptor side was more reduced than in either the pgr5-5 or trx x trx y1y2 mutant. After exposure to fluctuating light, the pgr5-5 trx x trx y1y2 mutant also showed more severe PSI photoinhibition. Furthermore, when plants were transferred from constant light to fluctuating light conditions for growth, the pgr5-5 trx x trx y1y2 mutant displayed pronounced photoinhibition, and its leaves bleached and died. These results indicate that the Trx system acts cooperatively with PSI-CET to protect PSI from photoinhibition under fluctuating light conditions.

Many proteins belonging into cryptochrome/photolyase family play important roles in regulating plant function, acting as either blue light photoreceptors or as enzymes responsible for repair of pyrimidine dimers produced under UV. The members of plant-specific photolyase/blue-light receptor 2 (PPL/PHR2) subclade of this family, are almost completely uncharacterized. Here, we focused on the role of protein encoded by Arabidopsis At2g47590 gene. Mutants in this gene have albino cotyledons, pale green true leaves and drastically delayed development. Based on this features we named At2g47590 gene: GERALT (GERMINATION ALBINO TRANSIENT). Using different approach including analysis of plant phenotypes, chloroplast sizes and architecture, transcriptomes, photosynthetic pigments, maximum PSII quantum yield (FV/FM) we show that the proper plant functioning is the effect of co-operation of GERALT-dependent and -independent pathways with the role of the former diminishing with plant age. Lower levels of transcripts dependent on plastid encoded polymerase and higher levels of these dependent on nuclear encoded polymerase, smaller chloroplasts with large grana stacks and very weakly developed stromal thylakoids, lower levels of photosynthetic pigments with higher chlorophyll a/b ratio, are among characteristic features of geralt plants. We believe that these results will encourage scientific community to study PPL/PHR2 proteins.

Carotenoids play dual roles in photosynthesis, extending light absorption and providing photoprotection through radical cation formation. Their ability to act as electron donors is defined by their redox potential for one-electron oxidation (Em). Here, we determine Em for carotenoids whose Em values are missing or inconsistently established in type-II reaction centers or associated antenna complexes, using a quantum chemical approach. The highest occupied molecular orbital (HOMO) energy levels correlated strongly with reported Em values in CH2Cl2, enabling determination of reliable Em values. All-trans isomers were found to be slightly stronger electron donors than their 15-cis counterparts. As this Em difference is small, the biological significance of cis isomerization appears to lie in pigment orientation rather than intrinsic redox properties. For xanthophyll-cycle pigments, a stepwise increase in Em from zeaxanthin to antheraxanthin to violaxanthin, attributable to their substituents, was revealed. Em values measured in micelles deviated markedly not only from those in CH2Cl2 but also from HOMO energy levels in water, questioning their relevance as reference values in protein environments. These results provide a unified framework for understanding carotenoid redox chemistry in photosynthesis.