Xin Liu

Leaf senescence is a comprehensive process performed by integrating various internal and external signals, followed by nutrient reallocation, especially via organic nitrogen (e.g., amino acids) mobilization. Amino acid (AA) transporters play an important role in crop growth and development by participating in the process of organic nitrogen remobilization. However, the biological functions and downstream effectors of amino acid transporters involved in leaf senescence are still poorly understood. In the present study, we cloned and characterized a cationic amino acid transporter gene, NtCAT1, from tobacco (K326). We found that NtCAT1 transcript levels were induced by age and abscisic acid (ABA). The NtCAT1 protein was highly localized in the plasma membrane. The overexpressing NtCAT1 line (OECAT1) showed early leaf senescence, accompanied with increased reactive oxygen species (ROS) and ABA content. By contrast, the NtCAT1 mutant (ntcat1-36) generated by the CRSPR/Cas9 system, showed a delayed-senescence phenotype with a decreased accumulation of ROS and ABA. Moreover, we discovered that the overexpression of NtCAT1 could downregulate the expression of the target of rapamycin (TOR) kinase gene and upregulate the transcript levels of ABA-related genes during leaf senescence compared with wild type (WT), while the expression of these genes in ntcat1-36 plants exhibited inverse trends. Furthermore, an analysis of the amino acid concentration demonstrated that NtCAT1 transgenic plants displayed dramatic changes in the amino acid profile during leaf senescence. In summary, our results suggest that NtCAT1 could promote leaf senescence via the increased biosynthesis of ABA, and our study provides new insights into the molecular mechanism of leaf senescence.

Soil salinity severely threatens plant growth and crop performance. Hydrogen sulfide (H₂S), a plant signal molecule, has been implicated in the regulation of plant responses to salinity stress. However, it is unclear how the transcriptional network regulates H₂S biosynthesis during salt stress response. In this study, we identify a rice NAC (NAM, ATAF and CUC) transcription factor, OsNAC35-like (OsNACL35), from a salt-tolerant cultivar ‘Sea Rice 86′ (SR86) and further show that it may have improved salt tolerance via enhanced H₂S production. The expression of OsNACL35 was significantly upregulated by high salinity and hydrogen peroxide (H₂O₂). The OsNACL35 protein was localized predominantly in the nucleus and was found to have transactivation activity in yeast. The overexpression of OsNACL35 (OsNACL35-OE) in japonica cultivar Nipponbare ramatically increased resistance to salinity stress, whereas its dominant-negative constructs (SUPERMAN repression domain, SRDX) conferred hypersensitivity to salt stress in the transgenic lines at the vegetative stage. Moreover, the quantitative real-time PCR analysis showed that many stress-associated genes were differentially expressed in the OsNACL35-OE and OsNACL35-SRDX lines. Interestingly, the ectopic expression of OsNACL35 triggered a sharp increase in H₂S content by upregulating the expression of a H₂S biosynthetic gene, OsDCD1, upon salinity stress. Furthermore, the dual luciferase and yeast one-hybrid assays indicated that OsNACL35 directly upregulated the expression of OsDCD1 by binding to the promoter sequence of OsDCD1. Taken together, our observations illustrate that OsNACL35 acts as a positive regulator that links H₂S production to salt stress tolerance, which may hold promising utility in breeding salt-tolerant rice cultivar.

Hydrogen sulfide (H₂S) has been shown to participate in various stress responses in plants, including drought, salinity, extreme temperatures, osmotic stress, and heavy metal stress. Manganese (Mn), as a necessary nutrient for plant growth, plays an important role in photosynthesis, growth, development, and enzymatic activation of plants. However, excessive Mn²⁺ in the soil can critically affect plant growth, particularly in acidic soil. In this study, the model plant Arabidopsis thaliana was used to explore the mechanism of H₂S participation and alleviation of Mn stress. First, using wild-type Arabidopsis with excessive Mn²⁺ treatment, the following factors were increased: H₂S content, the main H₂S synthetase L-cysteine desulfhydrase enzyme (AtLCD) activity, and the expression level of the AtLCD gene. Further, using the wild-type, AtLCD deletion mutant (lcd) and overexpression lines (OE5 and OE32) as materials, the phenotype of Arabidopsis seedlings was observed by exogenous application of hydrogen sulfide donor sodium hydrosulfide (NaHS) and scavenger hypotaurine (HT) under excessive Mn²⁺ treatment. The results showed that NaHS can significantly alleviate the stress caused by Mn²⁺, whereas HT aggravates this stress. The lcd mutant is more sensitive to Mn stress than the wild type, and the overexpression lines are more resistant. Moreover, the mechanism of H₂S alleviating Mn stress was determined. The Mn²⁺ content and the expression of the Mn transporter gene in the mutant were significantly higher than those of the wild-type and overexpression lines. The accumulation of reactive oxygen species was significantly reduced in NaHS-treated Arabidopsis seedlings and AtLCD overexpression lines, and the activities of various antioxidant enzymes (SOD, POD, CAT, APX) also significantly increased. In summary, H₂S is involved in the response of Arabidopsis to Mn stress and may alleviate the inhibition of Mn stress on Arabidopsis seedling growth by reducing Mn²⁺ content, reducing reactive oxygen species content, and enhancing antioxidant enzyme activity. This study provides an important basis for further study of plant resistance to heavy metal stress.

High temperature is one of the main abiotic stresses that threatens plant growth and development. Grapevine is one of the most economically important plants, and the production and quality of grapevine are often affected by some extreme climatic conditions, especially heat stress. However, the mechanisms of the response and adaptation of grapevine to heat stress are not well understood. Previously, we showed that a BON association protein from grapevine, VvBAP1, has a positive effect on cold tolerance. In the present study, we further explored the underlying physiological and molecular mechanisms of VvBAP1 in response to heat stress. The results indicated VvBAP1 was significantly induced by high temperature, and the expression of VvBAP1 in the resistant grapevine varieties was significantly higher than sensitive varieties. Overexpression of VvBAP1 in Arabidopsis significantly promoted the germination and growth of transgenic plants under heat stress, indicating that VvBAP1 has a positive role in the heat resistance. The chlorophyll content and net photosynthetic rate in the transgenic Arabidopsis was significantly higher than wild type. Overexpression of VvBAP1 also enhanced antioxidant enzymes activity and contributed to increase the expression of antioxidant enzyme genes, that to reduce the accumulation of reactive oxygen species and the lipid peroxidation under heat stress. In addition, the transcriptional activities of several heat stress response genes were increased in transgenic plants. In summary, we propose that VvBAP1 may play a potential important role in resistance against heat stress in grapevine, primarily through a combination of enhanced antioxidant activity and increased heat stress response genes expression.