Regulation of phenylpropanoid metabolism during moderate freezing and post-freezing recovery in Dendrobium officinale

Freezing injury is a major environmental limiting factor affecting plant yield and geographical distribution. Little is known about the regulation of phenylpropanoid metabolism during freezing (FT) and post-freezing recovery (FR). Dendrobium officinale is a valuable medicinal plant and hypersensitive to low temperature, especially freezing in winter. Here, we used metabolomics and transcriptomics analyses to reveal the regulation of of phenylpropanoid metabolism during FT and FR in D. officinale. Most anthocyanin and flavonol significantly increased during FR, including quercetin 3-O-glucoside (Q3G) and cyanidin 3-O-sophoroside (C3S) increased 104.6-fold and 66.8-fold in FR vs. CK. Transcriptomics analyses revealed the expression levels of flavonoid 3′- hydroxylase (F3`H) and flavonol synthase (FLS), which were related to an increase in quercetin derivatives. Six phytohormone-related GO terms were enriched during FT and FR. Four genes were significantly affected by FT and FR, including MYB97, MYB39, fructosyltransferase, and zinc finger transcript factor. Four GA response-related genes, 2-oxoglutarate-dependent dioxygenases, were specially induced during freezing stress. Moreover, jasmonic acid (JA) and salicylic acid (SA) were significantly increased during FT, and only SA decreased during FR. This study provided understanding of phenylpropanoid metabolism under freezing stress and will be useful for enhancing freezing tolerance via molecular breeding in D. officinale.