Iron deprivation affects aboveground cell wall biosynthesis in Populus and the role of PtrbHLH011 [RNA-seq]

Growing bioenergy crops like poplars on marginal land is appealing to minimize competition for arable land. However, this is hampered by a lack of insight into secondary cell wall (SCW) changes caused by environmental stress. Iron (Fe) deficiency is widespread and detrimental to plants. Here, we report that Fe deprivation increases SCW biosynthesis of poplar stem via the gene regulatory network (GRN) involving the transcription factor PtrbHLH011, whose expression is downregulated by Fe deprivation. PtrbHLH011 is a potent repressor of SCW, overexpression of which resulted in a reduction of stem SCW by over 65%. Furthermore, PtrbHLH011 overexpression induced foliar disease symptoms caused by reduced iron and flavonoid accumulations. By constructing PtrbHLH011-controlled GRN, we discovered that PtrbHLH011 binds to the AAAGACA sequence and represses essential genes for SCW biosynthesis, flavonoid biosynthesis, and iron homeostasis. Our results suggest that PtrbHLH011 functions as a co-regulator for the rapid activation of systematic Fe-deficiency responses. To study the biological impacts of iron deprivation on poplar, we treated poplar plants by either iron deprivation (0 µM Fe) or control (10 µM Fe) for 21 days in a hydroponic growth system. Tissues from young leaf and 3rd internode were then collected for total RNA extraction and paired-end 150 bp RNA-seq. Comparative gene expression profiling analysis of iron deprivation treated and control treated plants. To study the biological impacts of PtrbHLH011 overexpression, we extracted total RNAs from leaf and stem tissues of 4-month-old PtrbHLH011 overexpression and emptry vector control transgenic poplar plants. Paired-end 150 bp RNA-seq was performed. Comparative gene expression profiling analysis of PtrbHLH011 overexpression and empty vector control plants.