IDENTIFICATION OF PEPPER ABA CORE SIGNALING COMPONENTS AND THEIR ROLE IN SEED GERMINATION

Abscisic acid (ABA) plays an important role in various aspects of plant growth and development, such as adaptation to stresses (drought and high salinity), seed maturation and germination, and fruit development and ripening. The early stages of ABA signal transduction pathway have been established by identification of its core components: PYR/PYL/RCARs (PYLs), PP2Cs, and SnRK2s. Upon binding to ABA, the PYL receptors undergo a conformational change and become able to bind to and inhibit PP2C phosphatases. SnRK2 kinases are thus released from PP2C inhibition, become active and can phosphorylate downstream effectors, thus inducing transcription of ABA-responsive genes and, in guard cells, loss of turgor which results in closure of the stomata. Different studies have shown the potential applications of ABA signal core components to enhance plant drought resistance, through either genetic engineering or chemical approaches in crops. Here, we identify components of the C. annuum PYL, PP2C, and SnRK2 gene families. Using annotated tomato and Arabidopsis protein sequences, we isolated putative orthologs in pepper genome (C. annuum L Zunla-1). A dendrogram created through maximum likelihood method clusterized each PYL, PP2C, and SnRK2 gene family in subclasses. For further analyses we selected one PYL for each subfamily, three PP2Cs from different subclades and two SnRK2s from subclass III and one from subclass I. We measured the expression of these genes through qRT-PCR in seeds (cv Quadrato D'Asti giallo) incubated for four days with different concentrations of ABA or NaCl and observed an upregulation of most of the tested genes at high concentrations, including PYLs. Interestingly, the presence of NaCl or ABA had little or no effect on seed germination, measured in terms of radical emergence or cotyledon expansion. However, when seedling root growth was measured, after transfer from control media, sensitivity to ABA and salt was restored. Based on these results, our hypothesis is that pepper is insensitive to high concentrations of salt and ABA during the germination stage, due to the low expression of perception and signaling components. Further experiments will analyze in detail the mechanisms implicated in this phenomenon.