Comprehensive Analysis of Expressed Proteins in the Different Stages of the Style Development of Self-incompatible ‘Hyuganatsu’ (Citrus tamurana hort. ex Tanaka)

Abstract

In Citrus, self-incompatibility (SI) regulation is gametophytic, and this phenomenon is an economically critical problem for some Citrus cultivars without high parthenocarpic ability. Few molecular biological studies of SI in Citrus have been performed, and the molecular mechanism of SI has not been clarified. To investigate the effect of different stages of style development on pollen tube behavior, flower buds of self-incompatible 'Hyuganatsu' (Citrus tamurana hort. ex Tanaka) were histologically assayed. When the flower buds were observed 168 hours after pollination, pollen tubes in the self-pollinated flower buds 1 and 3 days before anthesis (DBA) were arrested in the upper part of the styles, while those in flower buds self-pollinated 5 DBA reached the base of the styles. These results revealed that SI in 'Hyuganatsu' has not yet occurred in the flower buds 5 DBA, but generated in the flower buds 3 DBA. To search SI-related pistil proteins in Citrus, we profiled a number of protein expressions in 'Hyuganatsu' styles of 1, 3, and 5 DBA by two-dimensional gel electrophoresis and MALDI-TOF mass spectrometry. One-hundred thirty-eight protein spots were significantly different in abundance among the three stages, and 17 up-regulated and 26 down-regulated protein spots could be identified. Among the 17 up-regulated proteins, nine up-regulated proteins exhibited the expression pattern of 1 DBA ≥ 3 DBA > 5 DBA, a pattern which reflected the transmission from SC to SI, evaluated by pollen tube growth. BLASTP homology search against the peptide sequences of these proteins was carried out and predicted the proteins related to the maintenance of cell shape, the signaling of pollen tube growth, the flavonol biosynthesis, the responses to various stresses, photosynthesis, and the methionine metabolic process. Among the nine proteins, some may be the SI-related pistil proteins; however, it was not possible to determine the SI-related key protein of the style in Citrus.

Self-incompatibility Related to Seedless Fruit Production in <i>Citrus</i> Plants

“…Some studies have reported the inhibition of self-pollen tubes found in the ovary (Ye et al, 2009). The inhibition of pollen tube growth has been observed in different locations in 'Hyuganatsu'-in the stigma (Yamashita, 1978), in the center of the style (Uchida et al, 2012), and at the bor-der between the stigma and style (Honsho et al, 2012). Some practical methods to break SI have been reported.…”

“…RNAseq was used for comparing no-, self-, and cross-pollination in the stigmas and styles of self-incompatible 'Xiangshui' lemon (Zhang et al, 2015). In 'Hyuganatsu', protein expression between different stages at 1-, 3-, and 5-day before anthesis was compared using 2D polyacrylamide gel electrophoresis (PAGE) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (Uchida et al, 2012).…”

Proteomics Advances in the Understanding of Pollen–Pistil Interactions

“…The first eight all participated in different biological processes while the last PG may be related to the SI reaction. The comparative studies in proteomics may be helpful in isolating the key proteins related to SI and eventually in explaining the reproduction process [ 76 ]. These studies uncover the special proteins in SC and/or SI process by proteomic approaches, which may also expand our insights on the possible pathways related to the interactions during both compatible and incompatible pollination.…”

Unreduced 2n Pollen Production in ‘Nishiuchi Konatsu’ Hyuganatsu as Inferred by Pollen Characteristics and Progeny Ploidy Level

“…Hyuganatsu occupies an important position as a late-season citrus cultivar in the fruit industry of Miyazaki prefecture. Hyuganatsu substantially has neither parthenocarpic traits nor self-compatibility (Miwa, 1951), for which approaches to genetic and molecular bases have recently begun Ngo et al, 2011;Uchida et al, 2012). As a result of these characteristics, a pollinizer is required to set the fruits, which ultimately contain many seeds (Yamamoto et al, 1995).…”