Comparative analysis of drought-responsive biochemical and transcriptomic mechanisms in two Dendrobium officinale genotypes

Drought stress is one of the most sever natural disaster, threatening to plant growth and global crop security. Dendrobium officinale is a drought-tolerance crop with effective defense mechanisms against drought stress, as well as an important economic plant for medicinal, cosmetic, or ornamental purposes. Revealing the regulatory mechanisms conferring drought resistance upon D. officinale is thus crucial for genetic breeding and water-saving agriculture. In this study, the biochemical and transcriptomic profiles of two D. officinale genotypes were comprehensively analyzed under three drought stress conditions. The M genotype has a relative weaker drought tolerance, as shown by withered leaves, rapidly accumulated malondialdehyde, and severely repressed expression of photosynthesis-related genes under water deficit. In the O genotype (drought-tolerant genotype), proline content, ascorbate peroxidase and catalase activities significantly increased with intensifying drought stress, showing a higher level than that in the M genotype, especially under severe drought stress. By contrast, superoxide dismutase and peroxidase activities were higher in the M genotype under moderate and severe water deficient. Transcriptome analysis demonstrated that mild water deficit initiated the plant hormone signal transduction pathway, while severe drought stress launched the flavonoid biosynthesis pathway in both D. officinale genotypes. Notably, high expression of most protein phosphatases type 2 C in the M genotype, a negative regulator of abscisic acid signaling, may partially explain the relative weaker drought tolerance of the M genotype. Moreover, the higher flavonoid content corresponding with the highly expressed PAL and DFR in the O genotype than in the M genotype, may confer a stronger drought tolerance upon the O genotype under water deficit. Additionally, the biased expression pattern of heat shock proteins, late embryogenesis abundant proteins, and dehydrins may also be linked to the different drought responses of the two D. officinale genotypes. Our results provide a theoretical basis for drought-tolerant crops breeding and water-sparing agriculture.