Seedling Growth and Transcriptional Responses to Salt Shock and Stress in Medicago sativa L., Medicago arborea L., and Their Hybrid (Alborea)

Abstract

Salinity is a major limiting factor in crop productivity worldwide. Medicago sativa L. is an important fodder crop, broadly cultivated in different environments, and it is moderately tolerant of salinity. Medicago arborea L. is considered a stress-tolerant species and could be an important genetic resource for the improvement of M. sativa’s salt tolerance. The aim of the study was to evaluate the seedling response of M. sativa, M. arborea, and their hybrid (Alborea) to salt shock and salt stress treatments. Salt treatments were applied as follows: salt stress treatment at low dose (50 mM NaCl), gradual acclimatization at 50–100 and 50–100–150 mM NaCl, and two salt shock treatments at 100 and 150 mM NaCl. Growth rates were evaluated in addition to transcriptional profiles of representative genes that control salt uptake and transport (NHX1 and RCI2A), have an osmotic function (P5CS1), and participate in signaling pathways and control cell growth and leaf function (SIMKK, ZFN, and AP2/EREB). Results showed that the studied population of M. sativa and M. arborea performed equally well under salt stress, whereas that of M. sativa performed better under salt shock. The productivity of the studied population of Alborea exceeded that of its parents under normal conditions. Nevertheless, Alborea was extremely sensitive to all initial salt treatments except the low dose (50 mM NaCl). In addition, significantly higher expression levels of all the studied genes were observed in the population of M. arborea under both salt shock and salt stress. On the other hand, in the population of M. sativa, NHX1, P5CS1, and AP2/EREB were highly upregulated under salt shock but to a lesser extent under salt stress. Thus, the populations of M. sativa and M. arborea appear to regulate different components of salt tolerance mechanisms. Knowledge of the different parental mechanisms of salt tolerance could be important when incorporating both mechanisms in Alborea populations.

Growth, Physiological, Biochemical, and Transcriptional Responses to Drought Stress in Seedlings of Medicago sativa L., Medicago arborea L. and Their Hybrid (Alborea)

“…Among the studied genes an AP2/EREB transcription factor belonging to the AINTEGUMENTA subgroup seems to be key player for the response of the studied populations to drought stress. Similar results were obtained from the study of the same population of the species under salt shock and stress [24]. Further research on the contribution of AINTEGUMENTA gene to abiotic tolerance is needed as there are only a few studies regarding its role to both salt and drought tolerance.…”

“…The population of M. arborea exhibited the highest induction of bzip transcription factor in both leaves and roots indicating that it is involved in its drought tolerance. On the other hand, the high induction of an AP2/EREB transcription factor belonging to the AINTEGUMENTA subgroup [24] highlights its importance regarding the response of the studied populations to drought stress. It is noteworthy that AINTEGUMENTA gene was the only gene that was highly expressed in roots of Alborea's population.…”

“…The seeds of M. arborea, M. sativa and Alborea used in the present study was obtained from E. Bingham from the Agronomy Department, University of -Madison-Wisconsin"Wisconsin, United States. The development of Alborea was described in detail by [22,24].…”

“…Seeds of parental species along with their hybrid (hereafter entries) were scarified as it was described by [24] Then the seeds were placed on agar plates, turned upside down and remained at 4 • C overnight. Finally, they were incubated to 20 • C for 3-4 days in the dark to ensure uniform germination.…”

“…In our previous work [24], transcriptional responses of several salt induced genes have been studied in the parent species and their hybrid. The aforementioned genes had been categorized into three groups: a. genes encoding ion transporters, intracellular Na + /H + antiporters (NHX1) and rare cold inducible2A (RCI2A), b. osmolytes, ∆1-pyrroline-5-carboxylate synthetase 1 (P5CS1) and c. transcription factors and signal transduction proteins, apetala2/ethylene-responsive element binding (AP2/EREB), stress-induced mitogen-activated protein kinases kinases(SIMKK), Zinc Finger (ZFN)).…”