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.

学界推测，表皮（epidermis）在植物发育过程中承担信号传导功能。一类表现出信号转导与径向模式建成缺陷的突变体属于固醇生物合成通路缺陷突变体。尽管已有认知认为活细胞依赖固醇，但目前仍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Δ8-Δ7异构酶；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，但本研究证实，HYD1基因在根表皮中的表达水平最高。在hyd1纯合突变体的表皮中特异性激活HYD1转录，可证明其在根模式建成与生长过程中发挥核心作用。在维管组织与根分生组织（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和PIN2生长素外运载体的模式建成恢复密切相关。研究认为，表皮在调控根生长与发育中的重要性，部分源于其作为固醇生物合成位点的功能，而生长素则是非细胞自主信号的候选介导因子。