Elucidating the role of key physio-biochemical traits and molecular network conferring heat stress tolerance in cucumber

MsSPL12 is a positive regulator in alfalfa (Medicago sativa L.) salt tolerance

KEY MESSAGE

Over expression of MsSPL12 improved alfalfa salt tolerance by reducing Na+ accumulation and increasing antioxidant enzyme activity and regulating down-stream gene expression. Improvement of salt tolerance is one of the major goals in alfalfa breeding. Here, we demonstrated that MsSPL12, an alfalfa transcription factor gene highly expressed in the stem cells, plays a positive role in alfalfa salt tolerance. MsSPL12 is localized in the nucleus and shows transcriptional activity in the presence of its C-terminus. To investigate MsSPL12 function in plant response to salt stress, we generated transgenic plants overexpressing either MsSPL12 or a chimeric MsSPL12-SRDX gene that represses the function of MsSPL12 by using the Chimeric REpressor gene-Silencing Technology (CRES-T), and observed that overexpression of MsSPL12 increased the salt tolerance of alfalfa transgenic plants associated with an increase in K+/Na+ ratio and relative water content (RWC) under salt stress treatment, but a reduction in electrolyte leakage (EL), reactive oxygen species (ROS), malondialdehyde (MDA), and proline (Pro) compared to wild type (WT) plants. However, transgenic plants overexpressing MsSPL12-SRDX showed an inhibited plant growth and a reduced salt tolerance. RNA-sequencing and quantitative real-time PCR analyses revealed that MsSPL12 affected the expression of plant abiotic resistance-related genes in multiple physiological pathways. The potential MsSPL12-mediated regulatory pathways based on the differentially expressed genes between the MsSPL12 overexpression transgenics and WT controls were predicted. In summary, our study proves that MsSPL12 is a positive regulator in alfalfa salt tolerance and can be used as a new candidate for manipulation to develop forage crops with enhanced salt tolerance.

A quick and effective method for thermostability differentiation in cucumber (Cucumis sativus L.)

High temperature affects the growth and production of cucumber. Selecting thermotolerant cucumber cultivars is conducive to coping with high temperatures and improving production. Thus, a quick and effective method for screening thermotolerant cucumber cultivars is needed. In this study, four cucumber cultivars were used to identify heat resistance indexes. The morphological, physiological and biochemical indexes were measured. When exposed to high temperatures, thermotolerant cucumber had a more stable photosystem, membrane, and oxidation-reduction systems. The impact of high temperatures on plants is multifaceted, and the accurate discrimination of heat resistance cannot be achieved solely based on a single or multiple indicators. Therefore, principal component analysis (PCA) was employed to comprehensively evaluate the heat resistance of cucumber plants. The results showed that the heat resistance obtained by PCA was significantly correlated with the heat injury index. In addition, the stepwise regression equation identified two heat-related indices, hydrogen peroxide content (H2 O2 ) and photosynthetic operating efficiency (Fq'/Fm'), and they can quickly distinguish the heat resistance of the other 8 cucumber cultivars. These results will help to accelerate the selection of thermotolerant resources and assist in cucumber breeding.