RESUMEN
The Actinidia (kiwifruit) is an emerging fruit plant that is severely affected by salt stress in northern China. Plants have evolved several signaling network mechanisms to cope with the detrimental effects of salt stress. To date, no reported work is available on metabolic and molecular mechanisms involved in kiwifruit salt tolerance. Therefore, the present study aims to decipher intricate adaptive responses of two contrasting salt tolerance kiwifruit species Actinidia valvata [ZMH (an important genotype), hereafter referred to as R] and Actinidia deliciosa ['Hayward' (an important green-fleshed cultivar), hereafter referred to as H] under 0.4% (w/w) salt stress for time courses of 0, 12, 24, and 72 hours (hereafter refered to as h) by combined transcriptome and metabolome analysis. Data revealed that kiwifruit displayed specific enrichment of differentially expressed genes (DEGs) under salt stress. Interestingly, roots of R plants showed a differential expression pattern for up-regulated genes. The KEGG pathway analysis revealed the enrichment of DEGs related to plant hormone signal transduction, glycine metabolism, serine and threonine metabolism, glutathione metabolism, and pyruvate metabolism in the roots of R under salt stress. The WGCNA resulted in the identification of five candidate genes related to glycine betaine (GB), pyruvate, total soluble sugars (TSS), and glutathione biosynthesis in kiwifruit. An integrated study of transcriptome and metabolome identified several genes encoding metabolites involved in pyruvate metabolism. Furthermore, several genes encoding transcription factors were mainly induced in R under salt stress. Functional validation results for overexpression of a candidate gene betaine aldehyde dehydrogenase (AvBADH, R_transcript_80484) from R showed significantly improved salt tolerance in Arabidopsis thaliana (hereafter referred to as At) and Actinidia chinensis ['Hongyang' (an important red-fleshed cultivar), hereafter referred to as Ac] transgenic plants than in WT plants. All in all, salt stress tolerance in kiwifruit roots is an intricate regulatory mechanism that consists of several genes encoding specific metabolites.
RESUMEN
Kiwifruit plants have a fleshy, shallow root system which is sensitive to waterlogging stress, which results in a decrease in crop yield or even plants death. Although the waterlogging stress responses in kiwifruit have attracted much attention, the underlying molecular mechanism remains unclear. In this study, waterlogging led to drastic inhibition of root growth of 'Donghong' kiwifruit (Actinidia chinensis) plants grown in vitro, which was accompanied by significant elevation of endogenous acetaldehyde and ethanol contents. RNA-seq of roots of plants waterlogged for 0, 1 and 2 days revealed that a total of 149 genes were up- or down-regulated, including seven biosynthetic genes related to the glycolysis/gluconeogenesis pathway and 10 transcription factors. Analyses with real-time PCR, dual-luciferase assays and EMSA demonstrated that AcERF74 and AcERF75, two members of the ERF-VII subfamily, directly upregulated AcADH1 (alcohol dehydrogenase). Moreover, the overexpression of AcERF74/75 in transgenic calli resulted in dramatic increase of endogenous ethanol contents through the triggering of AcADH1 and AcADH2 expression. Although the AcPDC2 (pyruvate decarboxylase) expression was also enhanced in transgenic lines, the endogenous acetaldehyde contents showed no significant changes. These results illustrated that AcERF74/75 are two transcriptional activators on alcoholic fermentation related genes and are responsive to waterlogging stress in kiwifruit.
