Temperature-Dependent Compatible and Incompatible Pollen-Style Interactions in Citrus clementina Hort. ex Tan. Show Different Transglutaminase Features and Polyamine Pattern

Abstract

In clementine, failure of fertilization can result in parthenocarpic fruit development, which has several advantages, such as seedless fruit, longer shelf-life, and greater consumer appeal. Recently, S-RNases have been identified in Citrus grandis , thus revealing that the self-incompatibility (SI) reaction relies on the S-RNase gametophytic mechanism. The fundamental role of environmental factors, mostly temperature, in determining the numbers of pollen tubes reaching the ovary is also well established in Citrus . In the present work, temperature-dependent pollen–pistil interactions in C. clementina were analyzed, focusing on several morphological aspects, as well as on polyamine (PA) content and the activity and distribution of transglutaminase (TGase), both reported to be involved in the SI response in pear and in pummelo. Results clearly indicate that temperature contributed to a different activation of the SI response, which occurs at optimal temperature of 25°C but was by-passed at 15°C. TGase activity was stimulated during the SI response, and it localized differently in the compatible and incompatible interaction: in compatible pollinated styles, TGase localized inside the style canal, while it was detected all around it in incompatible crosses. TGase localization and activity were congruent with the levels of soluble and insoluble conjugated PAs and with morphological evidences, which highlighted cell wall modification occurring as a result of SI.

Segregation Distortion for Male Parents in High Density Genetic Maps from Reciprocal Crosses between Two Self-Incompatible Cultivars Confirms a Gametophytic System for Self-Incompatibility in Citrus

“…The conclusion concerning a gametophytic SI system in citrus with the SI locus located at the beginning of chromosome 7 of the clementine reference genome proposed by Liang et al [46] is therefore strongly confirmed by our study. However, the influence of environmental conditions on pollen-pistil interactions has already been documented [41,73,74] and different transglutaminase features and polyamine pattern were recently described depending on the prevailing temperature during pollination [41]. Additional studies are needed to gain a full understanding of the pollen-pistil interaction in different citrus species under different environments.…”

“…Molecular and transcriptomic studies revealed that different molecules and gene families may be involved in SI mechanisms in citrus. Among the factors involved in the SI mechanism, a role for transglutaminases and polyamines and particularly spermidine was proposed [39][40][41]. Over the last 15 years, comparative transcriptome approaches have been applied to identify the genes and proteins involved in the SI response.…”

Parthenocarpy and Self-Incompatibility in Mandarins

“…indicate that constant high and low temperatures appear to have an effect on the incompatibility reaction by affecting the place where pollen tubes are arrested [59 cently, Aloisi et al [60] indicated that temperature contributed to a different activat the self-incompatibility reaction in C. clementina, occurring at an optimal temperatu 25 °C and bypassed at 15 °C. The incompatible reaction resulted in enhancement o transglutaminase enzyme activity and levels of conjugated polyamines when com to cross-pollination [60]. However, more research is needed to understand how env mental conditions can influence the self-incompatibility reaction in citrus.…”

Biochemical and Cytological Interactions Between Callose Synthase and Microtubules in the Tobacco Pollen Tube

“…In the pollen tube of Angiosperms, callose is deposited as a tubular sheath surrounding the pollen tube anks. Callose is usually absent at the apex and subapex of pollen tubes, and it is a common feature that incidental presence in those regions is associated with cessation of growth (Geitmann and Steer 2006;Mandrone et al 2019;Aloisi et al 2020). The tubular sheath of callose enhances the tensile strength of the cell wall.…”