Data from: Epidermal expression of a sterol biosynthesis gene regulates root growth by a non-cell autonomous mechanism in Arabidopsis

The epidermis is hypothesized to play a signalling role during plant development. One class of mutants showing defects in signal transduction and radial patterning are those in sterol biosynthesis. The expectation is that living cells require sterols, but it is not clear that all cell types express sterol biosynthesis genes. The HYDRA1 (HYD1) gene of Arabidopsis encodes sterol ∆8-∆7 isomerase, and although hyd1 seedlings are defective in radial patterning across several tissues, we show that the HYD1 gene is expressed most strongly in the root epidermis. Transgenic activation of HYD1 transcription in the epidermis of hyd1 null mutants reveals a major role in root patterning and growth. HYD1 expression in the vascular tissues and root meristem, though not endodermis or pericycle, also leads to some phenotypic rescue. Phenotypic rescue is associated with rescued patterning of the PIN1 and PIN2 auxin efflux carriers. The importance of the epidermis in controlling root growth and development is proposed to be in part due to its role as a site for sterol biosynthesis, and auxin is a candidate for the non-cell autonomous signal.

已有研究假说提出，表皮（epidermis）在植物发育过程中发挥信号传导功能。一类存在信号转导及径向模式建成缺陷的突变体，属于甾醇生物合成途径相关突变体。学界普遍认为活细胞依赖甾醇生存，但目前尚无法确定所有细胞类型均表达甾醇生物合成相关基因。拟南芥（Arabidopsis）的HYDRA1（HYD1）基因编码甾醇∆8-∆7异构酶（sterol ∆8-∆7 isomerase）；尽管hyd1突变体幼苗在多个组织中均存在径向模式建成缺陷，但本研究发现，HYD1基因在根表皮中的表达量最高。在hyd1纯合缺失突变体的表皮中通过转基因手段激活HYD1转录，可证实其在根系模式建成与生长过程中发挥核心作用。在维管组织与根尖分生组织（而非内皮层或中柱鞘）中表达HYD1，同样可实现部分表型恢复。该表型恢复与PIN1、PIN2生长素输出载体的模式建成恢复密切相关。现有研究提出，表皮调控根系生长发育的重要性，部分源于其作为甾醇生物合成位点的功能，而生长素则是潜在的非细胞自主信号分子。