Haizhen Ma

Low-temperature stress significantly limits wheat growth and productivity. Poly-γ-glutamic acid (γ-PGA) is an environmentally friendly green molecular material that plays an important role in plant growth and regulation; however, its protective mechanisms against cold stress in wheat remain poorly understood. In this study, the effect of γ-PGA on both chilling (4 °C) and freezing (−18 °C) resistance in wheat seedlings and its underlying mechanisms were comparatively studied. The results showed that the γ-PGA-treated seedlings exhibited a 128.81% higher survival rate after freezing stress and maintained significantly greater biomass accumulation under both stress conditions (62.44% and 26.56% higher dry weight under chilling and freezing stress, respectively). A physiological analysis revealed that γ-PGA enhanced osmoprotectant (proline and soluble sugars) accumulation and activated key antioxidant enzymes (SOD, POD, and APX). Then, an RNA-seq analysis identified 11,401 and 7721 differentially expressed genes under chilling and freezing stress, respectively, with 3598 common genes constituting a core cold-response network. KEGG and GO analyses demonstrated significant enrichment in pathways related to carbon metabolism, glutathione metabolism, phenylpropanoid–flavonoid biosynthesis, fatty acid metabolism, and cell wall organization. Notably, γ-PGA strongly upregulated key genes in phenylpropanoid–flavonoid metabolism (TraesCS2B02G615000 and TraesCS2B02G624400), glutathione metabolism (TraesCS1B02G127900), and lipid metabolism (TraesCS1B02G018700). These results provide comprehensive molecular insights into γ-PGA-mediated cold tolerance and support its potential application in sustainable wheat production under low-temperature stress conditions.

Soil salinity is a global issue threatening crop growth and yield. Salt-tolerant plant growth-promoting rhizobacteria (PGPB) can survive in high-salinity environments and help plants adapt to stress, thus serving as an effective measure to mitigate salt stress. In this study, a salt-tolerant plant growth-promoting bacterium, Halomonas alkaliantarcticae M23 (M23), was isolated from the rhizosphere soil of the salt-tolerant plant Suaeda salsa. This study characterized the effects of M23 on maize growth, salt stress response, and the composition and structure of rhizosphere soil microorganisms, and preliminary explained the mechanism by which M23 enhances maize salt tolerance. M23 can tolerate up to 14% NaCl, produce auxin, and exhibit the ability to absorb Na+ and accumulate K+ under salt stress. This study also measured amino acid production by M23 under different salinity conditions and found that M23 could mainly produce glutamic acid (Glu), glutamine, proline, and lysine, with their contents significantly increasing as salinity rises. Inoculating maize with M23 enhances the salt tolerance by increasing the K+/Na+ ratio, improving the antioxidant levels, and regulating its ABA levels in maize. Additionally, inoculating with strain M23 not only increases soil diversity but also alters the composition of bacterial communities in the maize rhizosphere soil. Most species were significantly enriched in saline soil treated with M23 at the phylum level. At the genus level, some salt-tolerant plant growth-promoting bacteria such as Bryobacter, Nocardioides, and Micromonosporaceae were also significantly enriched. Halomonas alkaliantarcticae M23 could promotes the salt tolerance of maize by increasing the K+/Na+ ratio, antioxidant levels, and ABA levels and changing the rhizosphere bacterial community. This study demonstrates that M23 has great potential in promoting plant growth in saline-alkali soils.