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。一类表现出信号转导（signal transduction）与径向模式建成（radial patterning）缺陷的突变体，属于固醇生物合成（sterol biosynthesis）相关突变体。尽管已知活细胞依赖固醇存活，但目前尚不清楚所有细胞类型均表达固醇生物合成基因。拟南芥（Arabidopsis）的HYDRA1（HYD1）基因编码固醇∆8-∆7异构酶（sterol ∆8-∆7 isomerase）；尽管hyd1幼苗在多个组织中均存在径向模式建成缺陷，但本研究证实，HYD1基因在根表皮中表达量最高。在hyd1无效突变体（hyd1 null mutants）的表皮中特异性激活HYD1转录，可揭示其在根系模式建成与生长中的核心作用。在维管组织（vascular tissues）及根尖分生组织（root meristem）中表达HYD1（而非内皮层（endodermis）或中柱鞘（pericycle）），同样可实现部分表型拯救。该表型拯救与PIN1、PIN2生长素输出载体（PIN1 and PIN2 auxin efflux carriers）的模式建成恢复密切相关。综上，表皮调控根系生长发育的重要性，部分源于其作为固醇生物合成位点的功能，而生长素（auxin）则是潜在的非细胞自主信号（non-cell autonomous signal）分子。