Abstract
To adapt and sense environmental perturbations, including a variety of biotic and abiotic stress conditions, plants have developed disparate regulatory pathways. Mitogen-activated protein kinase (MAPK or MPK) signaling cascades are found widespread across the eukaryotic kingdoms of life. In plants, they may regulate signaling pathways aimed at resisting the stressful effects of low temperature, salt damage, drought, touch, and mechanical damage. To date, no conclusive studies into Liriodendron chinense (Hemsl.) Sarg MPK-related stress resistance signaling have been performed. In our study, we cloned three homologous L. chinense MAP kinase kinase family genes: LcMKK2, LcMKK4, and LcMKK6. LcMKK2 and LcMKK6 have their highest expression level in the root, while LcMKK4 is highly expressed in the stem. LcMKK2 showed upregulation in response to salt and cold stress conditions in L. chinense. To further analyze its gene function, we overexpressed LcMKK2 in wild-type Arabidopsis thaliana (L.) Heynh. and obtained transgenic plants. Overexpression of LcMKK2 caused a significant reduction in plant mortality (from 96% to 70%) in response to a 7-day 200 mM NaCl treatment. Therefore, we conclude that LcMKK2 is involved in a signaling response to salt stress, and it could thus prove an effective target gene for breeding strategies to improve Liriodendron salt tolerance.
Highlights
Salt stress has a negative role in most plant growth and development; high salt causes a change in the osmotic potential or ion balance between the plant and its exterior environment, causing a water deficit and plant wilting
Given the importance of genes in the MAP kinase kinase (MAPKK) family under abiotic stresses, we wondered whether the function of these genes acts usefully in commercial timber tree species L. chinense
We isolated the MAPKKs from the leaves of L. chinense based on the MAPKK homologs of Arabidopsis from the NCBI database
Summary
Salt stress has a negative role in most plant growth and development; high salt causes a change in the osmotic potential or ion balance between the plant and its exterior environment, causing a water deficit and plant wilting. To respond to biotic or abiotic stresses, including salt stress, plants use a set of sophisticated signaling pathways [2]. The most studied salt stress regulatory pathways mainly include the MAPK (mitogen-activated protein kinase) signal pathway [3], the Ca2+ signaling transduction pathway [4], and the ABA signal pathway [5]. Transient activation of MAPK cascades is one of the first conserved defense responses playing an early triggering role in resistance caused by metabolic changes and transcriptional reprogramming [8].
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