Vascular transcription factors control epidermal responses to limiting phosphate conditions

Optimal plant growth is hampered by limiting amounts of the essential macronutrient phosphate in most soils. As a response, plant roots produce root hairs to capture this immobile nutrient. Although vital to high-yielding crops, this response remains poorly understood. By generating and exploiting a high spatial and temporal resolution single cell atlas of the Arabidopsis root, we show a remarkable enrichment of TMO5/LHW target genes in root hair epidermal cells. Moreover, these vascular bHLH factors are sufficient to induce a root hair formation response in the epidermal cells, similar as observed during low phosphate conditions, via the downstream cytokinin signaling. We further show that root hair formation under low phosphate conditions is almost absent when TMO5 function or cytokinin signaling is perturbed. In conclusion, cytokinin signaling links the adaptation of roots under low phosphate conditions in the epidermis to perception in vascular cells. Single-cell RNA-seq experiments were performed in triplicate on protoplast cells extracted from the root-tips of 6 day old Arabidopsis thaliana seedlings.

绝大多数土壤中可利用的必需大量营养元素磷酸盐含量有限，这会阻碍植物的最优生长。作为适应策略，植物根系会生成根毛以捕获这种难以移动的营养物质。尽管这一响应对高产作物至关重要，但目前人们对其分子调控机制仍知之甚少。本研究通过构建拟南芥（Arabidopsis thaliana）根系的高时空分辨率单细胞图谱，发现TMO5/LHW的靶基因在根毛表皮细胞中显著富集。此外，这些维管组织碱性螺旋-环-螺旋转录因子（bHLH）可通过下游细胞分裂素（cytokinin）信号通路，在表皮细胞中诱导根毛形成响应，这与低磷酸盐条件下观察到的现象一致。进一步实验表明，当TMO5功能或细胞分裂素信号通路受到干扰时，低磷酸盐条件下的根毛形成几乎完全消失。综上，细胞分裂素信号通路将表皮中根系对低磷酸盐条件的适应性响应，与维管细胞的感知过程关联起来。本研究对6日龄拟南芥幼苗根尖提取的原生质体细胞，开展了三次生物学重复的单细胞RNA测序（single-cell RNA-seq）实验。