Floral nectar of the obligate outcrossing Canavalia gladiata (Jacq.) DC. (Fabaceae) contains only one predominant protein, a class III acidic chitinase

Abstract

Floral nectar can affect the fitness of insect-pollinated plants, through both attraction and manipulation of pollinators. Self-incompatible insect-pollinated plants receive more insect visits than their self-compatible relatives, and the nectar of such species might face increased risk of infestation by pathogens carried by pollinators than self-compatible plants. Proteins in nectar (nectarins) play an important role in protecting the nectar, but little is known regarding nectarins in self-incompatible species. The nectarins from a self-incompatible and insect-pollinated leguminous crop, Canavalia gladiata, were separated using two-dimensional electrophoresis and analysed using mass spectrometry. The predominant nectarin gene was cloned and the gene expression pattern investigated using quantitative real-time PCR. Chitinolytic activity in the nectar was tested with different substrates. The C. gladiata nectar proteome only has one predominant nectarin, an acidic class III chitinase (CaChi3). The full-length CaChi3 gene was cloned, coding for a protein of 298 amino acids with a predicted signal peptide. CaChi3 is very similar to members of the class III chitinase family, whose evolution is dominated by purifying selection. CaChi3 was expressed in both nectary and leaves. CaChi3 has thermostable chitinolytic activity according to glycol-chitin zymography or a fluorogenic substratem but has no lysozyme activity. Chitinase might be a critical protein component in nectar. The extremely simple nectar proteome in C. gladiata disproves the hypothesis that self-incompatible species always have more complex nectar proteomes. Accessibility of nectar might be a significant determinant of the evolutionary pressure to develop nectar defence mechanisms.

Floral nectar chitinase is a potential marker for monofloral honey botanical origin authentication: A case study from loquat (Eriobotrya japonica Lindl.)

“…Chitinases have now been repeatedly identified in the floral nectar of different plant species, including important honey plants (Heil, 2011;Ma et al, 2017;Zha et al, 2016). Hence it is not surprising to detect chitinase activity in honey as in this study; indeed, it may be common in honey but have been previously overlooked.…”

“…Chitinase plays a direct role in plant defence by attacking the cell walls of bacteria, algae and fungi, and the exoskeletons of arthropods, within which chitin is a major component. It is hence deemed to be a pathogenesis-related protein implicated in defence mechanisms for reproductive organs, occurring in pollination drops, floral nectar and extrafloral nectar (Heil, 2011;Ma, Milne, Zhou, Fang, & Zha, 2017;Zha et al, 2016). However, there is as yet no empirical evidence showing that chitinases in nectar harms insect pollinators, such as honey bees (Zha et al, 2016).…”

Yeast–Bacterium Interactions: The Next Frontier in Nectar Research

“…[62, [78][79][80][81][82]. These chemicals are geographically and phylogenetically widespread across the plant kingdom, although species may vary in defense mechanisms [62,79].…”

Nectar- and stigma exudate-specific expression of an acidic chitinase could partially protect certain apple cultivars against fire blight disease

“…Basic class III chitinases frequently have dual chitinase and lysozyme activities, while the acidic class III chitinases have strong chitinase but only weak or no lysozyme activity (Ma et al 2017). To characterize the Machi3-1 protein, it was expressed in P. pastoris and then it was purified from the supernatant.…”

“…Indeed, in the proteome of stigma exudates, the defense and stressresponse proteins are the dominant GO categories (Sang et al 2012). Flower nectars frequently contain antimicrobial proteins in very high concentrations (Zha et al 2016;Ma et al 2017;Nogueira et al 2018;Schmitt et al 2018b) or accumulate nectarins that generate antimicrobial hydrogen peroxide in the nectar (Carter et al 2007). It was shown that nectar of wild squash is antibiotic and efficiently reduces the symptoms of the bacterial wilt (Sasu et al 2010).…”