CoNPR1 and CoNPR3.1 are involved in SA- and MeSA- mediated growth of the pollen tube in Camellia oleifera

Abstract

Salicylic acid (SA) is a plant hormone involved in a series of growth, development, and stress responses in plants. Nonexpressor of pathogenesis-related genes 1 (NPR1) is the core regulatory gene in the process of SA-mediated systemic acquired resistance (SAR). Whether NPR1 is involved in pollen tube growth mediated by SA and its derivative MeSA (methyl salicylate) remains to be explored. Here, we found that the contents of endogenous SA and MeSA in self- or cross-pollinated pistils changed significantly, and exogenous SA and MeSA significantly promoted pollen germination and pollen tube elongation of Camellia oleifera at lower concentrations. CoNPR1, CoNPR3.1, CoNPR3.2, and CoNPR5 were identified, and they were all located in the nucleus. A high level of consistency was observed across the phylogenetic relationships, gene structures, and functional domains, indicating a clear division of function, as observed in other species. The expression levels of CoNPR1, CoNPR3.1, CoNPR3.2, and CoNPR5 in self- and cross-pollinated pistils had certain regularity. Furthermore, they exhibited tissue-specific expression pattern. CoNPR1 and CoNPR3.1 were expressed in pollen tubes, whose expression was regulated by SA or MeSA, and their expression patterns were basically consistent with the trend of pollen germination. These results indicate that SA and MeSA are involved in the pollen tube growth of C. oleifera, and CoNPRs may play an important role therein.