Abstract
Abscisic acid (ABA) plays an important role in various aspects of plant growth and development, including adaptation to stresses, fruit development and ripening. In seeds, ABA participates through its core signaling components in dormancy instauration, longevity determination, and inhibition of germination in unfavorable environmental conditions such as high soil salinity. Here, we show that seed germination in pepper was delayed but only marginally reduced by ABA or NaCl with respect to control treatments. Through a similarity search, pepper orthologs of ABA core signaling components PYL (PYRABACTIN RESISTANCE1-LIKE), PP2C (PROTEIN PHOSPHATASE2C), and SnRK2 (SUCROSE NONFERMENTING1 (SNF1)-RELATED PROTEIN KINASE2) genes were identified. Gene expression analyses of selected members showed a low abundance of PYL and SnRK2 transcripts in dry seeds compared to other tissues, and an up-regulation at high concentrations of ABA and/or NaCl for both positive and negative regulators of ABA signaling. As expected, in hydroponically-grown seedlings exposed to NaCl, only PP2C encoding genes were up-regulated. Yeast two hybrid assays performed among putative pepper core components and with Arabidopsis thaliana orthologs confirmed the ability of the identified proteins to function in ABA signaling cascade, with the exception of a CaABI isoform cloned from seeds. BiFC assay in planta confirmed some of the interactions obtained in yeast. Altogether, our results indicate that a low expression of perception and signaling components in pepper seeds might contribute to explain the observed high percentages of seed germination in the presence of ABA. These results might have direct implications on the improvement of seed longevity and vigor, a bottleneck in pepper breeding.
Highlights
Pepper (Capsicum spp.) is an economically important genus of the Solanaceae family, with a global production of 38.4 million tons including green fruits and dried pods, harvested from 3.7 million hectares in 20161
To verify the sensitivity of Capsicum annuum to abiotic stress and Abscisic acid (ABA) treatments at the seed stage, we scored the germination percentage of commercial seeds of Quadrato D’Asti giallo (QA), 2https://www.genome.jp/tools-bin/clustalw 3http://www.ch.embnet.org/software/BOX_form.html a high yielding variety among the most commonly cultivated for marketing in Italy and abroad
The germination rates in terms of radicle emergence and cotyledon expansion of seeds in presence of ABA or NaCl were analyzed in detail (Figure 1)
Summary
Pepper (Capsicum spp.) is an economically important genus of the Solanaceae family, with a global production of 38.4 million tons including green fruits and dried pods, harvested from 3.7 million hectares in 20161. Seed germination starts with the uptake of water by imbibition of the dry seed, followed by embryo expansion. A further increase in water uptake (phase III) happens only when germination occurs, as the embryo axis elongates and breaks through the covering layers, typically the endosperm and the testa (Manz et al, 2005). While in Arabidopsis thaliana testa and endosperm rupture occur simultaneously, in many Solanaceae seeds these two events are temporally distinct (Petruzzelli et al, 2003). The accumulation of βGlu occurs prior to radicle emergence. Unfavorable osmotic potentials, darkness and ABA inhibit endosperm rupture and βGlu accumulation in the micropylar cap of the seeds, the site of radicle emergence (Petruzzelli et al, 2003)
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