Ethylene Enhances Seed Germination and Seedling Growth Under Salinity by Reducing Oxidative Stress and Promoting Chlorophyll Content via ETR2 Pathway.

Alfalfa (Medicago sativa L.) is an important forage, and salinity is a major stress factor on its yield. In this study, we show that osmotic stress retards alfalfa seedling growth, while ionic/oxidative stress reduces its seed germination. Ethylene treatment can recover the germination rate of alfalfa seeds under salt stress, while ethylene inhibitor silver thiosulfate exacerbates salt effects. ETH reduces the accumulation of MDA and H2O2 and increases POD activity. ETH and ACC improve the salt tolerance of alfalfa by increasing proline content under salt stress. In contrast, STS inhibits alfalfa seed germination by reducing POD activity. NaCl treatment reduces chlorophyll content in alfalfa leaves, while ETH and ACC can increase the chlorophyll content and promote seedling growth. ETH promotes the growth of alfalfa in saline condition by reducing the expression of MsACO and MsERF8 genes, while increases its germination rate by upregulating MsERF11 gene. Silencing of MsETR2, a putative ethylene receptor gene in alfalfa, abolishes ethylene triggered tolerance to salt stress. In summary, we show that ethylene improves salt tolerance in alfalfa via MsETR2 dependent manner, and we also analyze the regulatory mechanism of ethylene during germination of alfalfa seeds under salt stress.

Corrigendum: Ethylene Enhances Seed Germination and Seedling Growth Under Salinity by Reducing Oxidative Stress and Promoting Chlorophyll Content via ETR2 Pathway.

[This corrects the article DOI: 10.3389/fpls.2020.01066.].

miR403a and SA Are Involved in NbAGO2 Mediated Antiviral Defenses Against TMV Infection in Nicotiana benthamiana.

RNAi (RNA interference) is an important defense response against virus infection in plants. The core machinery of the RNAi pathway in plants include DCL (Dicer Like), AGO (Argonaute) and RdRp (RNA dependent RNA polymerase). Although involvement of these RNAi components in virus infection responses was demonstrated in Arabidopsis thaliana, their contribution to antiviral immunity in Nicotiana benthamiana, a model plant for plant-pathogen interaction studies, is not well understood. In this study, we investigated the role of N. benthamiana NbAGO2 gene against TMV (Tomato mosaic virus) infection. Silencing of NbAGO2 by transient expression of an hpRNA construct recovered GFP (Green fluorescent protein) expression in GFP-silenced plant, demonstrating that NbAGO2 participated in RNAi process in N. benthamiana. Expression of NbAGO2 was transcriptionally induced by both MeSA (Methylsalicylate acid) treatment and TMV infection. Down-regulation of NbAGO2 gene by amiR-NbAGO2 transient expression compromised plant resistance against TMV infection. Inhibition of endogenous miR403a, a predicted regulatory microRNA of NbAGO2, reduced TMV infection. Our study provides evidence for the antiviral role of NbAGO2 against a Tobamovirus family virus TMV in N. benthamiana, and SA (Salicylic acid) mediates this by induction of NbAGO2 expression upon TMV infection. Our data also highlighted that miR403a was involved in TMV defense by regulation of target NbAGO2 gene in N. Benthamiana.

Cloning and characterization of a Ca(2+)/H(+) exchanger from the halophyte Salicornia europaea L.

The calcium ion (Ca(2+)), which functions as a second messenger, plays an important role in plants' responses to various abiotic stresses, and Ca(2+)/H(+) exchangers (CAXs) are an important part of this process. In this study, we isolated and characterized a putative Ca(2+)/H(+) exchanger gene (SeCAX3) from Salicornia europaea L., a succulent, leafless euhalophyte. The SeCAX3 open reading frame was 1368 bp long and encoded a 455-amino-acid polypeptide that showed 67.9% similarity to AtCAX3. SeCAX3 was expressed in the shoots and roots of S. europaea. Expression of SeCAX3 was up-regulated by Ca(2+), Na(+), sorbitol, Li(+), abscisic acid, and cold treatments in shoots, but down-regulated by Ca(2+), sorbitol, abscisic acid, and cold treatments in roots. When SeCAX3 was transformed into a Ca-sensitive yeast strain, the transformed cells were able to grow in the presence of 200 mM Ca(2+). Furthermore, SeCAX3 conferred drought, salt, and cold tolerance in yeast. Compared with the control strains, the yeast transformants expressing SeCAX3 were able to grow well in the presence of 30 mM Li(+), 150 mM Mg(2+), or 6 mM Ba(2+). These results showed that the expression of SeCAX3 in yeast suppressed its Ca(2+) hypersensitivity and conferred tolerance to Mg(2+) and Ba(2+). Together, these findings suggest that SeCAX3 might be a Ca(2+) transporter that plays a role in regulating cation tolerance and the responses of S. europaea to various abiotic stresses.