Regulation of phenylpropanoid biosynthesis by MdMYB88 and MdMYB124 contributes to pathogen and drought resistance in apple

Abstract

MdMYB88 and MdMYB124 have been demonstrated to be responsible for lignin accumulation in apple under drought stress. In this study, using a metabolomic approach, we identified differentially accumulated phenylpropanoid and flavonoid metabolites in MdMYB88/124 transgenic RNAi plants under control and long-term drought stress conditions in apple roots. We confirmed the regulation of phenylalanine by MdMYB88 and MdMYB124 via UPLC-MS in apple roots under both control and drought conditions. Using Electrophoretic Mobility Shift Assay (EMSA) and ChIPquantitative PCR (qPCR) analyses, we found that MdMYB88 positively regulates the MdCM2 gene, which is responsible for phenylalanine biosynthesis, through binding to its promoter region. Under long-term drought conditions, MdMYB88/124 RNAi plants consistently accumulated increased amounts of H 2 O 2 and MDA, while MdMYB88 and MdMYB124 overexpression plants accumulated decreased amounts of H 2 O 2 and MDA. We also examined the accumulation of metabolites in the phenylpropanoid biosynthesis pathway in the leaves of MdMYB88 and MdMYB124 transgenic apple plants after long-term drought stress. We found that metabolites responsible for plant defense, including phenylpropanoids and flavonoids, accumulated less in the RNAi plants but more in the overexpression plants under both control and drought conditions. We further demonstrated that MdMYB88/124 RNAi plants were more sensitive to Alternaria alternata f. sp. mali and Valsa mali, two pathogens that currently severely threaten apple production. In contrast, MdMYB88 and MdMYB124 overexpression plants were more tolerant to these pathogens. The cumulative results of this study provided evidence for secondary metabolite regulation by MdMYB88 and MdMYB124, further explained the molecular roles of MdMYB88 and MdMYB124 in drought resistance, and provided information concerning molecular aspects of their roles in disease resistance.

Integrated transcriptome and small RNA sequencing analyses reveal a drought stress response network in Sophora tonkinensis

“…Functional analysis showed that DEGs were significantly enriched in the phenylpropanoid biosynthesis pathway. Phenylpropanoids exert a significant effect on plant responses to drought stress [ 28 – 30 ]. Key genes in the phenylpropanoid biosynthesis pathway have previously been shown to be modulated in drought-treated basil ( Ocimum basilicum L.) , a traditional medicinal plant [ 28 ].…”

Contribution of phenylpropanoid metabolism to plant development and plant–environment interactions

“…In apple, MdMYB88 and MdMYB124 are induced by drought stress and bind to the promoters of MdVND6 and MdMYB46 , which are positive regulators of lignin deposition (Geng et al, 2018). In addition, MdMYB88 positively regulates the phenylalanine biosynthesis by binding to the promoter of the MdCM2 gene, which is required for phenylalanine biosynthesis, thereby providing more precursors for phenylpropanoid metabolism (Geng et al, 2020a). It was also reported that drought induces the expression of CmCAD1 , 2 , and 3 to enhance lignin deposition, which is critical for guaranteeing efficient axial water transport and barrier of lateral water flow in oriental melon (Liu et al, 2020).…”

Apple Sumo E3 Ligase Mdsiz1 Negatively Regulates Drought Tolerance

“…Hence, it is important to understand the function of key drought-responsive genes and investigate the physiologic mechanisms by which apple trees respond to drought [5,6] . Plants may respond to drought stress by controlling stomatal movement [7] , hormone biosynthesis [8] , the ability to scavenge reactive oxygen species [9] , accumulation of metabolic products [10] , root development [3] , transcriptional regulation [10] and microRNA biogenesis [11] .…”