CRPs are numerous in plants, with 756 CRP-encoding genes in the Arabidopsis thaliana genome.[7] Several CRPs bind known receptors,[8] but most CRP signaling mechanisms and protein interactions are uncharacterized. Characterized CRPs function as short-range intercellular signals during processes such as plant defense, bacterial symbiosis, stomatal patterning, fertilization, vegetative tissue development, and seed development.[4]
Many CRPs function in plant defense. Defensins, a major class of CRP with an eight-cysteine motif forming four disulfide bridges,[9] are involved in pathogen response.[4] Other putative antimicrobial CRPs include lipid transfer proteins, thionins, knottins, heveins, and snakins. Additionally, some CRPs have allergenic, ɑ-amylase inhibitory, or protease inhibitory functions that deter herbivores.[9]
In plant reproduction, CRPs are involved in pollen tube growth and guidance[10] and early embryo patterning,[11] in addition to other functions. Among those involved in pollen tube attraction are the LUREs, a group of ovular pollen-tube attractants in Arabidopsis thaliana and Torenia fournieri[12] that preferentially attract conspecific pollen,[10] and STIG1, a CRP expressed in the stigma of Solanum lycopersicum that interacts with the pollen-specific receptor PRK2.[8] In early embryo development, CRPs such as ESF1 are necessary for suspensor development and normal seed morphology.[11]
^Huang Q, Dresselhaus T, Gu H, Qu LJ (June 2015). "Active role of small peptides in Arabidopsis reproduction: Expression evidence". Journal of Integrative Plant Biology. 57 (6): 518–21. doi:10.1111/jipb.12356. PMID25828584.