Regulation of water transport in Arabidopsis by methyl jasmonate

The impact of insect egg deposition on Pinus sylvestris transcriptomic and phytohormonal responses to larval herbivory

Plants can improve their resistance to feeding damage by insects if they have perceived insect egg deposition prior to larval feeding. Molecular analyses of these egg-mediated defence mechanisms have until now focused on angiosperm species. It is unknown how the transcriptome of a gymnosperm species responds to insect eggs and subsequent larval feeding. Scots pine (Pinus sylvestris L.) is known to improve its defences against larvae of the herbivorous sawfly Diprion pini L. if it has previously received sawfly eggs. Here, we analysed the transcriptomic and phytohormonal responses of Scots pine needles to D. pini eggs (E-pine), larval feeding (F-pine) and to both eggs and larval feeding (EF-pine). Pine showed strong transcriptomic responses to sawfly eggs and-as expected-to larval feeding. Many egg-responsive genes were also differentially expressed in response to feeding damage, and these genes play an important role in biological processes related to cell wall modification, cell death and jasmonic acid signalling. EF-pine showed fewer transcriptomic changes than F-pine, whereas EF-treated angiosperm species studied so far showed more transcriptional changes to the initial phase of larval feeding than only feeding-damaged F-angiosperms. However, as with responses of EF-angiosperms, EF-pine showed higher salicylic acid concentrations than F-pine. Based on the considerable overlap of the transcriptomes of E- and F-pine, we suggest that the weaker transcriptomic response of EF-pine than F-pine to larval feeding damage is compensated by the strong, egg-induced response, which might result in maintained pine defences against larval feeding.

How the xerophytic moss Pogonatum inflexum tolerates desiccation

KEY MESSAGE

Desiccation-tolerant process of xerophytic moss Pogonatum inflexum were identified through de novo transcriptome assembly , morphological structure and physiology analysis. Pogonatum inflexum (Lindb.) Lac. is a typical xerophytic moss and have been widely used in gardening and micro-landscape. However, the mechanisms underlying desiccation tolerance are still unclear. In this study, morphological,  physiological and trancriptomic analyses of P. inflexum to tolerate desiccation were carried out. Our results indicate that P. inflexum increase osmoregulation substances, shut down photosynthesis, and alter the content of membrane lipid fatty acids in response to desiccation, and the genes involved in these biological processes were changes in expression after desiccation. 12 h is the threshold for P. inflexum to tolerate desiccation and its photosynthesis has not been damaged within 12 h of desiccation and can still recover after rewater. We also proved that the gametocyte of P. inflexum has the ability to absorb and transport water, and contains lignin-synthesis genes in response to tolerant desiccation. Our findings not only explain the mechanisms of P. inflexum during desiccation, but also provide some attractive candidate genes for genetic breeding.

Salicylic Acid Modulates the Osmotic System and Photosynthesis Rate to Enhance the Drought Tolerance of Toona ciliata

Toona ciliata M. Roem. is a valuable and fast-growing timber species which is found in subtropical regions; however, drought severely affects its growth and physiology. Although the exogenous application of salicylic acid (SA) has been proven to enhance plant drought tolerance by regulating the osmotic system and photosynthesis rate, the physiological processes involved in the regulation of drought tolerance by SA in various plants differ. Therefore, drought mitigation techniques tailored for T. ciliata should be explored or developed for the sustainable development of the timber industry. We selected 2-year-old T. ciliata seedlings for a potting experiment, set the soil moisture at 45%, and subjected some of the T. ciliata seedlings to a moderate drought (MD) treatment; to others, 0.5 mmol/L exogenous SA (MD + SA) was applied as a mitigation test, and we also conducted a control using a normal water supply at 70% soil moisture (CK). Our aim was to investigate the mitigating effects of exogenous SA on the growth condition, osmotic system, and photosynthesis rate of T. ciliata under drought stress conditions. OPLS-VIP was used to analyze the main physiological factors that enable exogenous SA to alleviate drought-induced injury in T. ciliata. The results indicated that exogenous SA application increased the growth of the ground diameter, plant height, and leaf blades and enhanced the drought tolerance of the T. ciliata seedlings by maintaining the balance of their osmotic systems, improving their gas exchange parameters, and restoring the activity of their PSII reaction centers. The seven major physiological factors that enabled exogenous SA to mitigate drought-induced injury in the T. ciliata seedlings were the soluble proteins (Sp), net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), stomatal opening window (Sow), activity of the photosystem II reaction center (ΦPSII), and electron transfer rate (ETR). Of these, Sp was the most dominant factor. There was a synergistic effect between the osmotic system and the photosynthetic regulation of drought injury in the T. ciliata seedlings. Overall, our study confirms that exogenous SA enhances the drought tolerance of T. ciliata by modulating the osmotic system and photosynthesis rate.

Salinity Tolerance of Halophytic Grass Puccinellia nuttalliana Is Associated with Enhancement of Aquaporin-Mediated Water Transport by Sodium

In salt-sensitive plants, root hydraulic conductivity is severely inhibited by NaCl, rapidly leading to the loss of water balance. However, halophytic plants appear to effectively control plant water flow under salinity conditions. In this study, we tested the hypothesis that Na⁺ is the principal salt factor responsible for the enhancement of aquaporin-mediated water transport in the roots of halophytic grasses, and this enhancement plays a significant role in the maintenance of water balance, gas exchange, and the growth of halophytic plants exposed to salinity. We examined the effects of treatments with 150 mM of NaCl, KCl, and Na₂SO₄ to separate the factors that affect water relations and, consequently, physiological and growth responses in three related grass species varying in salt tolerance. The grasses included relatively salt-sensitive Poa pratensis, moderately salt-tolerant Poa juncifolia, and the salt-loving halophytic grass Puccinellia nuttalliana. Our study demonstrated that sustained growth, chlorophyll concentrations, gas exchange, and water transport in Puccinellia nuttalliana were associated with the presence of Na in the applied salt treatments. Contrary to the other examined grasses, the root cell hydraulic conductivity in Puccinellia nuttalliana was enhanced by the 150 mM NaCl and 150 mM Na₂SO₄ treatments. This enhancement was abolished by the 50 µM HgCl₂ treatment, demonstrating that Na was the factor responsible for the increase in mercury-sensitive, aquaporin-mediated water transport. The observed increases in root Ca and K concentrations likely played a role in the transcriptional and (or) posttranslational regulation of aquaporins that enhanced root water transport capacity in Puccinellia nuttalliana. The study demonstrates that Na plays a key role in the aquaporin-mediated root water transport of the halophytic grass Puccinellia nuttalliana, contributing to its salinity tolerance.

Hormonal and environmental signaling pathways target membrane water transport

Plant water transport and its molecular components including aquaporins are responsive, across diverse time scales, to an extremely wide array of environmental and hormonal signals. These include water deficit and abscisic acid (ABA) but also more recently identified stimuli such as peptide hormones or bacterial elicitors. The present review makes an inventory of corresponding signalling pathways. It identifies some main principles, such as the central signalling role of ROS, with a dual function of aquaporins in water and hydrogen peroxide transport, the importance of aquaporin phosphorylation that is targeted by multiple classes of protein kinases, and the emerging role of lipid signalling. More studies including systems biology approaches are now needed to comprehend how plant water transport can be adjusted in response to combined stresses.

Plant aquaporins: A frontward to make crop plants drought resistant

Drought stress alters gene expression and causes cellular damage in crop plants. Drought inhibits photosynthesis by reducing the content and the activity of the photosynthetic carbon reduction cycle, ultimately decreasing the crop yield. The role of aquaporins (AQP) in improving the growth and adaptation of crop plants under drought stress is of importance. AQP form channels and control water transport in and out of the cells and are associated with drought tolerance mechanisms. The current review addresses: (1) the evolution of AQPs in plants, (2) the classification of plant AQPs, (3) the role of AQPs in drought alleviation in crop plants, and (4) the phytohormone crosstalk with AQPs in crops exposed to drought stress.