Castorina Giulia, Fox Samantha, Tonelli Chiara, Galbiati Massimo, Conti Lucio
Dipartimento di Bioscienze, Università degli studi di Milano, Via Celoria 26, 20133, Milan, Italy.
Department of Cell and Developmental Biology, John Innes Centre, Norwich, NR4 7UH, UK.
BMC Plant Biol. 2016 Aug 2;16(1):172. doi: 10.1186/s12870-016-0851-z.
Guard cells (GCs) are specialised cells within the plant epidermis which form stomatal pores, through which gas exchange can occur. The GCs derive through a specialised lineage of cell divisions which is specified by the transcription factor SPEECHLESS (SPCH), the expression of which can be detected in undifferentiated epidermal cells prior to asymmetric division. Other transcription factors may act before GC specification and be required for correct GC patterning. Previously, the DOF transcription factor STOMATAL CARPENTER 1 (SCAP1) was shown to be involved in GC function, by activating a set of GC-specific genes required for GC maturation and activity. It is thus far unknown whether SCAP1 can also affect stomatal development.
Here we show that SCAP1 expression can also be observed in young leaf primordia, before any GC differentiation occurs. The study of transgenic plants carrying a proSCAP1:GUS-GFP transcriptional fusion, coupled with qPCR analyses, indicate that SCAP1 expression peaks in a temporal window which is coincident with expression of stomatal patterning genes. Independent scap1 loss-of-function mutants have a reduced number of GCs whilst SCAP1 over expression lines have an increased number of GCs, in addition to altered GC distribution and spacing patterns. The study of early markers for stomatal cell lineage in a background carrying gain-of-function alleles of SCAP1 revealed that, compared to the wild type, an increased number of protodermal cells are recruited in the GC lineage, which is reflected in an increased number of meristemoids.
Our results suggest an early role for SCAP1 in GC differentiation. We propose that a function of SCAP1 is to integrate different aspects of GC biology including specification, spacing, maturation and function.
保卫细胞（GCs）是植物表皮内的特化细胞，它们形成气孔，气体可通过气孔进行交换。保卫细胞通过特定的细胞分裂谱系产生，该谱系由转录因子“无言”（SPCH）指定，在不对称分裂之前，未分化的表皮细胞中可检测到其表达。其他转录因子可能在保卫细胞特化之前起作用，是正确的保卫细胞模式形成所必需的。此前，DOF转录因子气孔木匠1（SCAP1）被证明通过激活一组保卫细胞成熟和活性所需的保卫细胞特异性基因，参与保卫细胞功能。到目前为止，尚不清楚SCAP1是否也能影响气孔发育。
在这里，我们表明在任何保卫细胞分化发生之前，在幼叶原基中也可观察到SCAP1的表达。对携带proSCAP1:GUS-GFP转录融合的转基因植物的研究，结合qPCR分析，表明SCAP1的表达在一个时间窗口达到峰值，该窗口与气孔模式形成基因的表达一致。独立的scap1功能丧失突变体的保卫细胞数量减少，而SCAP1过表达系除了保卫细胞分布和间距模式改变外，保卫细胞数量增加。对具有SCAP1功能获得等位基因背景下的气孔细胞谱系早期标记的研究表明，与野生型相比，更多的原表皮细胞被招募到保卫细胞谱系中，这反映在更多的分生细胞上。
我们的结果表明SCAP1在保卫细胞分化中起早期作用。我们提出，SCAP1的一个功能是整合保卫细胞生物学的不同方面，包括特化、间距、成熟和功能。
