ABSTRACT
Root development influences plant responses to environmental conditions, and well-developed rooting enhances plant survival under abiotic stress. However, the molecular and genetic mechanisms underlying root development and abiotic stress tolerance in plants remain unclear. In this study, we identified the MYB transcription factor-encoding gene IbMYB73 by cDNA-amplified fragment length polymorphism and RNA-seq analyses. IbMYB73 expression was greatly suppressed under abiotic stress in the roots of the salt-tolerant sweet potato (Ipomoea batatas) line ND98, and its promoter activity in roots was significantly reduced by abscisic acid (ABA), NaCl, and mannitol treatments. Overexpression of IbMYB73 significantly inhibited adventitious root growth and abiotic stress tolerance, whereas IbMYB73-RNAi plants displayed the opposite pattern. IbMYB73 influenced the transcription of genes involved in the ABA pathway. Furthermore, IbMYB73 formed homodimers and activated the transcription of ABA-responsive protein IbGER5 by binding to an MYB binding sites I motif in its promoter. IbGER5 overexpression significantly inhibited adventitious root growth and abiotic stress tolerance concomitantly with a reduction in ABA content, while IbGER5-RNAi plants showed the opposite effect. Collectively, our results demonstrated that the IbMYB73-IbGER5 module regulates ABA-dependent adventitious root growth and abiotic stress tolerance in sweet potato, which provides candidate genes for the development of elite crop varieties with well-developed root-mediated abiotic stress tolerance.
Subject(s)
Abscisic Acid , Ipomoea batatas , Abscisic Acid/pharmacology , Abscisic Acid/metabolism , Ipomoea batatas/genetics , Ipomoea batatas/metabolism , Plants, Genetically Modified/metabolism , Amplified Fragment Length Polymorphism Analysis , Stress, Physiological/physiology , Gene Expression Regulation, Plant , Plant Proteins/genetics , Plant Proteins/metabolismABSTRACT
Plant flavonoids are valuable natural antioxidants. Sweet potato (Ipomoea batatas) leaves are rich in flavonoids, regenerate rapidly, and can adapt to harsh environments, making them an ideal material for flavonoid biofortification. Here, we demonstrate that the B-box (BBX) family transcription factor IbBBX29 regulates the flavonoid contents and development of sweet potato leaves. IbBBX29 was highly expressed in sweet potato leaves and significantly induced by auxin (IAA). Overexpression of IbBBX29 contributed to a 21.37%-70.94% increase in leaf biomass, a 12.08%-21.85% increase in IAA levels, and a 31.33%-63.03% increase in flavonoid accumulation in sweet potato, whereas silencing this gene produced opposite effects. Heterologous expression of IbBBX29 in Arabidopsis (Arabidopsis thaliana) led to a dwarfed phenotype, along with enhanced IAA and flavonoid accumulation. RNA-seq analysis revealed that IbBBX29 modulates the expression of genes involved in the IAA signaling and flavonoid biosynthesis pathways. Chromatin immunoprecipitation-quantitative polymerase chain reaction and electrophoretic mobility shift assay indicated that IbBBX29 targets key genes of IAA signaling and flavonoid biosynthesis to activate their expression by binding to specific T/G-boxes in their promoters, especially those adjacent to the transcription start site. Moreover, IbBBX29 physically interacted with developmental and phenylpropanoid biosynthesis-related proteins, such as AGAMOUS-LIKE 21 protein IbAGL21 and MYB308-like protein IbMYB308L. Finally, overexpressing IbBBX29 also increased flavonoid contents in sweet potato storage roots. These findings indicate that IbBBX29 plays a pivotal role in regulating IAA-mediated leaf development and flavonoid biosynthesis in sweet potato and Arabidopsis, providing a candidate gene for flavonoid biofortification in plants.