The Involvement of Antioxidant Enzyme System, Nitrogen Metabolism and Osmoregulatory Substances in Alleviating Salt Stress in Inbred Maize Lines and Hormone Regulation Mechanisms.

Salt stress inhibited the growth of maize. B46 and NC236 were chosen as materials and NaCl concentrations (0, 55, 110, 165, and 220 mmol L-1) were set. We found the activities of SOD, POD, CAT, APX, GR, MDHAR, and DHAR decreased under NaCl stress. Compared with NC236, the contents of AsA and GSH, AsA/DHA and GSH/GSSG of B46 decreased. The content of O2-, H2O2, MDA, and EL of B46 increased. The contents of NO3- and NO2- decreased, while the content of NH4+ increased under high NaCl concentration. The activities of NR and NiR decreased, while the activities of GS and GOGAT increased first and then decreased. For B46 and NC236, the maximum of NADH-GDH and NAD-GDH appeared at 165 and 110 mmol L-1 NaCl concentration, respectively. Compared with B46, and the GOT and GPT activities of NC236 increased first and then decreased. With the increase of NaCl concentration, the contents of proline, soluble protein, and soluble sugar were increased. The Na+ content of B46 and NC236 increased, and the K+ content and K+/Na+ decreased. Compared with NC236, B46 had higher IAA content in leaf, higher Z + ZR content in leaf and root, and lower ABA content in leaf and root.

Comparative transcriptome analysis of salt-sensitive and salt-tolerant maize reveals potential mechanisms to enhance salt resistance.

BACKGROUND: Salt stress is a devastating environmental stress that causes plant growth inhibition and yield reduction. OBJECTIVE: The identification of salt-tolerant genes brings hope for the generation of salinity-tolerant crop plants through molecular breeding. METHODS: In this study, one salt-sensitive and one salt-tolerant maize inbred line were screened from 242 maize inbred lines. Reactive oxygen species (ROS)-related enzyme activities were detected and salt-responsive comparative transcriptome analysis was performed for control and 220 mM NaCl treated maize leaves. RESULTS: Salt-tolerant maize inbred line (L87) showed higher ROS-related enzyme (SOD, POD, APX and CAT) activities and accumulated relatively lower levels of ROS under salt stress. Of the total DEGs, 1856 upregulated DEGs were specific to L87, including stress tolerance-related members of the 70kDa family of heat shock proteins (Hsp70s) and aquaporins. The DEGs involved in the abscisic acid (ABA), ethylene, jasmonic acid (JA) and salicylic acid (SA) signal transduction pathways may determine the difference in salt tolerance between the two varieties, especially one central component SnRK2, that positively regulates ABA signaling and was only upregulated in L87. Analysis of DEGs related to ROS scavenging showed that some peroxidase (POD), glutathione S-transferase (GST), catalase (CAT) and superoxide dismutase (SOD) genes specific to L87 probably enhanced its salt tolerance. The analysis of differentially expressed transcription factors (TFs) suggested that WRKY TFs could contribute to the difference in salt tolerance between the two maize lines. CONCLUSION: Compared with Salt-sensitive maize inbred line (L29), L87 exhibits specific regulatory mechanisms related to salt tolerance, including plant hormone interactions, ROS scavenging and the regulation of TFs. Our study identifies new candidate genes that may regulate maize tolerance to salt stress and provides useful information for breeding maize with high salt resistance.

Genome-wide association study Identified multiple Genetic Loci on Chilling Resistance During Germination in Maize.

Maize (Zea mays, L.) cultivation has expanded greatly from tropical to temperate zones; however, its sensitivity to chilling often results in decreased germination rates, weak seedlings with reduced survival rates, and eventually lower yields. We conducted germination tests on the maize-282-diverse-panel (282 inbred lines) under normal (25 °C) and chilling (8 °C) conditions. Three raw measurements of germination were recorded under each condition: 1) germination rate, 2) days to 50% germination, and 3) germination index. Three relative traits were derived as indicators of cold-tolerance. By using the 2,271,584 single nucleotide polymorphisms (SNPs) on the panel from previous studies, and genome-wide association studies by using FarmCPU R package to identify 17 genetic loci associated with cold tolerance. Seven associated SNPs hit directly on candidate genes; four SNPs were in high linkage disequilibrium with candidate genes within 366 kb. In total, 18 candidate genes were identified, including 10 candidate genes supported by previous QTL studies and five genes supported by previous gene cloning studies in maize, rice, and Arabidopsis. Three new candidate genes revealed by two associated SNPs were supported by both QTL analyses and gene cloning studies. These candidate genes and associated SNPs provide valuable resources for future studies to develop cold-tolerant maize varieties.