Abstract
ABSTRACTStomata are highly specialized epidermal structures that control transpiration and gas exchange between plants and the environment. Signal networks underlying stomatal development have been previously uncovered but much less is known about how signals involved in stomatal development are transmitted to RNA polymerase II (Pol II or RPB), which plays a central role in the transcription of mRNA coding genes. Here, we identify a partial loss-of-function mutation of the third largest subunit of nuclear DNA-dependent Pol II (NRPB3) that exhibits an increased number of stomatal lineage cells and paired stomata. Phenotypic and genetic analyses indicated that NRPB3 is not only required for correct stomatal patterning, but is also essential for stomatal differentiation. Protein-protein interaction assays showed that NRPB3 directly interacts with two basic helix-loop-helix (bHLH) transcription factors, FAMA and INDUCER OF CBF EXPRESSION1 (ICE1), indicating that NRPB3 serves as an acceptor for signals from transcription factors involved in stomatal development. Our findings highlight the surprisingly conserved activating mechanisms mediated by the third largest subunit of Pol II in eukaryotes.
Highlights
Stomata, which consist of paired guard cells, are known to have played crucial roles in the colonization of land by plants
Phenotypic analysis and cloning of nrpb3-1 To identify new genes involved in stomatal development, we isolated a mutant with increased stomatal density and paired stomata in an ethyl methanesulfonate mutagenesis screen
By examining the time course of stomatal differentiation in germinating cotyledons with the stomatal lineage reporter TMMpro::TOO MANY MOUTHS (TMM)-GFP (Nadeau and Sack, 2002b), we found that the mutant cotyledons produced larger stomatal lineage cell clusters and more stomatal lineage cells compared with the wild type at each developmental stage
Summary
Stomata, which consist of paired guard cells, are known to have played crucial roles in the colonization of land by plants. Turgordriven stomatal movement requires ion and water exchange with neighboring cells and controls transpiration and gas exchange between plants and the environment. The development of stomata complies with the one-cell-spacing rule, that is, two stomata are separated by at least one non-stomatal cell. In Arabidopsis, the stomatal lineage begins with an asymmetric entry division, which takes place in a fraction of protodermal cells known as meristemoid mother cells (MMCs). The division gives rise to two daughter cells with distinct morphologies: a large sister cell known as the stomatal lineage ground cell (SLGC) and a small triangular meristemoid. The meristemoid undergoes asymmetric amplifying division and regenerates an SLGC and a meristemoid that converts into a guard mother cell (GMC).
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