About CRIP / Cysteine-Rich:
Cysteine-rich proteins are also commonly referred to as cysteine-rich peptides, CRPs and disulphide-rich peptides. They are small proteins that contain a large number of cysteines and stabilise the protein's tertiary structure in one of two ways. They either cross-link to form disulphide bonds (these cysteine rich proteins typically have an even number of cysteines) or bind metal ions by chelation. It’s worth noting that cysteine-rich proteins contain a highly conserved secretion peptide signal at the N-terminus. They also contain a cysteine-rich region at the C-terminus.
Cysteine- rich proteins often tend to be numerous in plants. In fact, there are 756 CRP-encoding genes in the Arabidopsis thaliana genome. They often function in the plant’s defence. Some have allergenic, an amylase inhibitory or protease inhibitory functions that deter herbivores. Others function as short-range intercellular signals during processes including: Bacterial symbiosis, Stomatal patterning, Fertilization, Vegetative tissue development, Seed development.
When it comes to plant reproduction, cysteine rich proteins are significantly involved in processes such as pollen tube growth and guidance and early embryo patterning. However, this isn’t the full extent of their functions. Among the cysteine-rich proteins that are involved in pollen tube attraction are LUREs. These are a group of ovular pollen-tube attractants in Arabidopsis thaliana and Torenia fournieri. They preferentially attract conspecific pollen, and STIG1, a CRP expressed in the stigma of Solanum lycopersicum that interacts with the pollen-specific receptor PRK2. In regards to early embryo development, CRPs such as ESF1, are absolutely necessary for processes such as suspensor development and normal seed morphology.