Abscisic acid controlled sex before transpiration in vascular plants

Abstract

Sexual reproduction in animals and plants shares common elements, including sperm and egg production, but unlike animals, little is known about the regulatory pathways that determine the sex of plants. Here we use mutants and gene silencing in a fern species to identify a core regulatory mechanism in plant sexual differentiation. A key player in fern sex differentiation is the phytohormone abscisic acid (ABA), which regulates the sex ratio of male to hermaphrodite tissues during the reproductive cycle. Our analysis shows that in the fern Ceratopteris richardii, a gene homologous to core ABA transduction genes in flowering plants [SNF1-related kinase2s (SnRK2s)] is primarily responsible for the hormonal control of sex determination. Furthermore, we provide evidence that this ABA-SnRK2 signaling pathway has transitioned from determining the sex of ferns to controlling seed dormancy in the earliest seed plants before being co-opted to control transpiration and CO 2 exchange in derived seed plants. By tracing the evolutionary history of this ABA signaling pathway from plant reproduction through to its role in the global regulation of plant-atmosphere gas exchange during the last 450 million years, we highlight the extraordinary effect of the ABA-SnRK2 signaling pathway in plant evolution and vegetation function.OST1 | fern | stomata | evolution | sex determination

Fern Stomatal Responses to ABA and CO2 Depend on Species and Growth Conditions

“…The components of the core stomatal ABA signaling pathway have been shown to be present in mosses, lycophytes, ferns, and angiosperms (Hanada et al, 2011;Cai et al, 2017), indicating an early origin of ABA signal transduction. Nevertheless, it is possible that not all of these proteins have strictly stomata-related functions in ferns, as was shown recently for a homolog of the OST1 kinase that participates in sex determination in a fern (McAdam et al, 2016). However, other kinases besides OST1 can activate anion channels toward stomatal closure, and although OST1 is the most important among them in Arabidopsis (Kollist et al, 2014), ABAinduced signaling pathways do not have to be identical in ferns and angiosperms.…”

“…These data indicate that the core stomatal ABA-signaling pathway is conserved in plants. Recently, a homolog of OST1 was shown to regulate sex determination in the fern Ceratopteris richardii (McAdam et al, 2016), suggesting that at least some of the components of the ABA-signaling pathway that control stomatal responses in angiosperms could have different or additional functions in ferns. Moreover, the ABA signal transduction pathways of ferns and angiosperms may be at least partly different; thus, the analysis of fern homologs of components involved in ABA-response pathways of angiosperms is not sufficient to fully understand the mechanisms of ABA responsiveness in ferns.…”

Stomatal Function across Temporal and Spatial Scales: Deep-Time Trends, Land-Atmosphere Coupling and Global Models

“…2). However, some disagreement remains on whether stomatal ABA sensitivity is universal (McAdam et al, 2016).…”

<div class="page" title="Page 1"><div class="layoutArea"><div class="column">Structure, function and evolution of stomata from a bryological perspective</div></div></div>

“…Moreover, it is difficult to determine if the responses noted are due to passive movement of water or active hormonal control. Several studies point to passive closing of stomata in response to low water status in lycophytes and ferns without ABA involvement (Brodribb & McAdam 2011, McAdam et al 2016. Higher concentrations of ABA in liverworts and hornworts are associated with dry conditions suggesting that stomatal closure may be an overall stress response (Hartung et al 1987).…”

“…Closing of stomata in response to ABA involves activation of SLAC1 anion channel by OST1 and although genes that encode these elements are present in the green alga Klebsormidium, the liverwort Marchantia and the moss Physcomitrella, only in Physcomitrella do both elements, PpOST1 and PpSLAC1, form a functional complex that activates the anion channel similar to angiosperms (Lind et al 2015). These components of the ABA dependent drought stress response originated before the diversification of embryophytes but it is still controversial when the use of this gene regulatory network was employed for stomata function , Lind et al 2015, McAdam et al 2016.…”