Arabidopsis cysteine-rich receptor-like protein kinase CRK33 affects stomatal density and drought tolerance.

Cysteine-rich receptor-like protein kinases (CRKs) are transmembrane proteins containing two domains of unknown function 26 (DUF26) RLKs in their ectodomain. Despite that CRKs control important aspects of plant development, only few proteins have functionally been characterized. In this work, we analyzed the function of CRK33 by characterizing two insertional lines. The stomatal density and stomatal index were decreased in crk33-2 and crk33-3 plants in comparison to wild-type plants, correlating with a decreased transpiration in transgenic plants and a higher drought tolerance. Furthermore, photosynthesis and stomatal conductance changed. Finally, all four stomata cell fate genes were upregulated, especially the expression of TMM and SPCH in the mutant background, suggesting a role for CRK33 in stomatal spacing.

Gene expression of an arabinogalactan lysine-rich protein CaAGP18 during vegetative and reproductive development of bell pepper (Capsicum annuum L.).

Lysine-rich (Lys-rich) proteins encoded by AGP17, AGP18, and AGP19 genes are cell wall-associated glycopeptides related to sexual reproduction in flowering plants. This subclass belongs to classical arabinogalactan proteins (AGPs) widely studied in model plants like Arabidopsis. In this study, we identified the CaAGP18 cDNA from bell pepper (Capsicum annuum L.), as well as its expression pattern during vegetative and reproductive development. The deduced amino acid sequence revealed a Lys-rich AGP18 protein of 238 amino acids residues in length with an estimated molecular mass of 22.85 kDa and an isoelectric point of 9.7. The protein is predicted as canonical AGP due to the presence of a small Lys-rich region and a C-terminal sequence essential for posttranslational modification with a glycosylphosphatidylinositol (GPI). Phylogenetic analysis showed that CaAGP18 is clustered together with NtAGP18, SpAGP18, StAGP18 and NaAGP18 from Solanaceae species. CaAGP18 expression through plant phenological stages had the highest transcription level in leaves at the seedling stage, whereas in reproductive organs there was a significant up-regulation in pistils during anthesis, also in petals 2 days post-anthesis (DPA), and in fruit at the expansion stage. Our results open future research for possible roles of CaAGP18 in cell expansion as a wall-associated plasticizer and reproductive processes like pistil interactions and petal cell death.