Proteomic Analysis Of Two Maize Inbred Lines That Differ Significantly In The Salt Stress Response And Mapping QTLs For Salt Tolerance

Salinity is a major abiotic stress throughout the world. Nearly one-third of cultivated land has been affected by salinity in China, which caused a reduction of more than15%of the annual grain production. Maize(Zea mays L.) plays an important role in global food security and economic development. Unfortunately, maize is not a salt-tolerant crop, especially at the seedling stage. Therefore, better understanding the salt responsive mechanisms in maize seedling is critical for improving maize salt tolerance. In the present study, we performed physiological, proteomic and genetic analysis of salt tolerance in maize based on two maize inbred lines that differ significantly in salt stress. The studies may provide the basis for salt tolerance molecular mechanisms in maize, and the QTLs identified here could be helpful to improve salt tolerance in maize by marker-assisted selection (MAS). The main results were as follows:(1) To explore variations in salt tolerance,162maize inbred lines were screened in soil compartments containing0.3%(w/v) NaCl. The most salt-tolerant line F63and the most salt-sensitive line F35were selected under salinity condition. The results were validated well within the hydroponic system under160mM NaCl treatment.(2) Physiological analysis showed that high concentrations of NaC1increased relative electrolytic leakage and reduced shoot length, shoot fresh weight, relative water content, and K+/Na+ratio in maize. However, the degrees to which maize plants reacted to salt stress were different in different inbred lines. F63exhibited a smaller increase in relative electrolytic leakage and less of reduction in the K+/Na+ratio under NaCl treatment than F35, demonstrating that F63could maintain membrane integrity and ion homeostasis more successfully than F35. The low osmotic potential enabled F63to retain more water and a high relative water content in response to salt treatment. Therefore, F63exhibited a better growth status than F35under salt stress. (3) Proteomic analysis revealed that47proteins were increased and46proteins were decreased in F63,27proteins were increased and22proteins were decreased in F35in response to salt stress. It was suggested that more proteins were induced in salt-tolerant line F63under salt stress. Fourteen proteins had similar induction patterns in these two lines, and they were mainly involved in hormone regulation, stress/defense and water conservation, indicating that these lines might employ common mechanisms in response to salt stress. However, most proteins exhibited different induction patterns, and they were mainly involved in oxidative stress, protein synthesis and regulation, as a result, F63were more tolerant than F35. The differentially expressed proteins identified in this study were functionally validated in yeast.(4) We developed a RIL population derived from a cross F63x F35and constructed a genetic linkage map using1011SNPs. QTL analysis was conducted under saline field and the hydroponic culture conditions at the seedling stage. For unconditional QTL analysis, we detected twenty additive and nine epistatic QTLs, of which twelve and two showed significant QTL x treatment interaction effects, respectively. Moreover, the use of conditional analysis model allowed us to be able to detect nine condition QTLs. Five unconditional and three conditional QTLs reportected here could individually explain more than20%of the phenotypic variation. The QTLs identified here could be helpful to improve salt tolerance in maize by MAS.