Development‐related changes of protein ubiquitination in pollen from male and female kiwifruit (Actinidia deliciosa)

Abstract

Kiwifruit (Actinidia deliciosa) is a dioecious vine whose staminate and pistillate flowers nonetheless develop non-functional reproductive structures of the opposite sex. Ubiquitin is a small, highly conserved protein found in all eucaryotes: a covalent ATP-dependent attachment of ubiquitin marks proteins for degradation. In the present paper, we used immunoblotting to investigate the presence of free ubiquitin and ubiquitin conjugates during pollen development in male (androfertile) and in female (androsterile) genotypes of kiwifruit. In the male, several high molecular mass protein conjugates were present throughout development. On the contrary, such a pattern characterized only early stages of pollen from the female genotype, where conjugates progressively disappeared, until they were detectable only in trace amounts at anthesis. The highest content of conjugates in the male genotype was observed when microspores were approaching the first mitosis, Free ubiquitin increased continuously during development of the male microgametophyte so that mature pollen contained considerable amounts of the ubiquitin monomer at the time of its release from the anther, By contrast, only low levels were detectable in the degenerating microspores in the pistillate flowers. In vitro experiments using labeled ubiquitin indicated that early-uninucleate microspores of the female genotype had a much higher conjugation rate Ban those of the male genotype at the same stage. However, after feeding alpha-lactalbumin as exogenous substrate, the rate of ubiquitin conjugation strongly increased and was quite similar in both sexes. Nuclear features of pollen development in both genotypes are also described. The nucleus progressively degenerated in the microspores of the pistillate flowers starting from the early-uninucleate stage, in parallel with the progressive decrease in ubiquitin content and activity, At anthesis, the microspores in the pistillate flowers either had no nucleus or showed only traces of chromatin, Thus, the ubiquitin system seems to play an important role in protein turnover occurring during the normal developmental pathway of the kiwifruit microgametophyte, while it was mainly involved in regressive events related to microspore degeneration in the female genotype

Inhibition of Proteasome Activity Strongly Affects Kiwifruit Pollen Germination. Involvement of the Ubiquitin/Proteasome Pathway as a Major Regulator

“…Ubiquitin and ubiquitinprotein conjugates have been found in virtually all gymnosperm and angiosperm pollen examined, suggesting a role for the ubiquitin proteolytic system in pollen development and maturation (Kulikauskas et al, 1995;Scoccianti et al, 1999aScoccianti et al, , 1999b). Here we provide the first evidence, based not only on the detection of free ubiquitin and ubiquitin conjugates, but mostly on a functional analysis of the 26S proteolytic complex responsible for the turnover of ubiquitinated proteins, that the ubiquitin system is strongly involved in pollen germination and tube growth in kiwifruit.…”

“…deliciosa). The ubiquitin monomer continuously increases during pollen development and reaches the highest level at the time of pollen release (Scoccianti et al, 1999a(Scoccianti et al, , 1999b. It is interesting that the reduction in free ubiquitin observed in maize Ky 21 inbred and olive pollen does not coincide with a parallel reduction in ubiquitin transcripts (Callis and Bedinger, 1994;Alché et al, 2000).…”

Polyploidy enhances F1 pollen sterility loci interactions that increase meiosis abnormalities and pollen sterility in autotetraploid rice

“…The ubiquitination pathway is known to function in signaling, transcription, DNA repair, cell viability, and endosomal trafficking (Bader and Steller, 2009;Li et al, 2012). Os02g0490000 is required for normal pollen development in kiwifruit (Actinidia deliciosa; Scoccianti et al, 1999). Thus, we speculated that down-regulation of Os02g0490000 may affect pollen development of autotetraploid rice hybrids.…”

Genetic Resources of Kiwifruit: Domestication and Breeding

“…Female plants produce morphologically perfect flowers with well-developed pistils and stamens (Plate 1.2D), but their stamens produce nonviable pollen; flowers of male plants have small, rudimentary ovaries (Plate 1.2C) without viable ovules but their stamens release viable pollen (Rizet 1945;Schmid 1978;White 1990). Pistil development in staminate flowers stops at an early stage (Brundell 1975;Schmid 1978;Polito and Grant 1984;Watanabe and Takahashi 1984) whereas pollen development in pistillate flowers stops at a very late stage of development (White 1990;Messina 1993;Scoccianti et al 1999;Coimbra et al 2004). This type of floral mimicry, in which unrewarding pistillate flowers mimic pollen-producing staminate flowers, is known as cryptic dioecy (Schmid 1978), and the stamens of pistillate flowers are important in attracting pollinating insects (Kawagoe and Suzuki 2004).…”