Early Transcriptomic Adaptation to Na2CO3 Stress Altered the Expression of a Quarter of the Total Genes in the Maize Genome and Exhibited Shared and Distinctive Profiles with NaCI and High pH Stresses

Sodium carbonate （Na2CO3） presents a huge challenge to plants by the combined damaging effects of Na＋, high pH, and CO32. Little is known about the cellular responses to Na2CO3 stress. In this study, the transcriptome of maize （Zea mays L. cv. B73） roots exposed to Na2CO3 stress for 5 h was compared with those of NaCI and NaOH stresses. The expression of 8,319 genes, representing over a quarter of the total number of genes in the maize genome, was altered by Na2CO3 stress, and the downregulated genes （5,232） outnumbered the upregulated genes （3,087）. The effects of Na2CO3 differed from those of NaCI and NaOH, primarily by downregulating different categories of genes. Pathways commonly altered by Na2CO3, NaCI, and NaOH were enriched in phenylpropanoid biosynthesis, oxidation of unsaturated fatty acids, ATP- binding cassette （ABC） transporters, as well as the metabolism of secondary metabolites. Genes for brassinosteroid biosynthesis were specifically upregulated by Na2CO3, while genes involved in ascorbate and aldarate metabolism, protein processing in the endoplasmic reticulum and by N-glycosylation, fatty acid biosynthesis, and the circadian rhythm were downregulated. This work provides the first holistic picture of early transcriptomic adaptation to Na2CO3 stress, and highlights potential molecular pathways that could be manipulated to improve tolerance in maize.