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Yifan Chen, Qian Bai, Funan Ruan and Shuchai Su

The Pistacia chinensis Bunge is traditionally dioecious, and the female trees are more required to grow in practice for oil seed production. The discovery of monoecious P. chinensis Bunge in North China provided good raw materials to study the sex differentiation process. The objective of this study was to identify the differently expressed proteins in flower buds in two key sex differentiation phases in monoecious P. chinensis Bunge. Morphological observation and paraffin section were used to determine the key phenophases, and label-free quantitative technique was used for proteomic analysis. The results showed that the proteins related to oxidative stress resistance up-regulated while proteins involved in photosynthesis down-regulated during the female primordium differentiation in bisexual flower buds of the monoecious P. chinensis Bunge in early March, while proteins related to oxidative stress resistance, ribosome activity, and photosynthetic function up-regulated during the male primordium differentiation in bisexual flower buds of the monoecious P. chinensis Bunge in late May. The most up-regulated proteins all involved in the photosynthesis pathway in both kind of flower buds in late May compared to those in early March, and the down-regulated proteins all involved in the ribosome pathway. The identified differentially expressed proteins such as the Cu/Zn superoxide dismutases may be possible molecular markers for sex determination in monoecious P. chinensis Bunge.

Nils Bareither, André Scheffel and Johannes Metz

ABSTRACT

The ecological benefits of polyploidy are intensely debated. Some authors argue that plants with duplicated chromosome sets (polyploids) are more stress-resistant and superior colonizers and may thus outnumber their low ploidy conspecifics in more extreme habitats. Brachypodium distachyon (sensu lato), for example, a common annual grass in Israel and the entire Mediterranean basin, comprises three cytotypes of differing chromosome numbers that were recently proposed as distinct species. It was suggested that increased aridity increases the occurrence of its polyploid cytotype.

Here, we tested at two spatial scales whether polyploid plants of B. distachyon s.l. are more frequently found in drier habitats in Israel. We collected a total of 430 specimens (i) along a large-scale climatic gradient with 15 thoroughly selected sites (spanning 114–954 mm annual rainfall), and (ii) from corresponding Northern (more mesic) and Southern (more arid) hill slopes to assess the micro-climatic difference between contrasting exposures. Cytotypes were then determined via flow cytometry.

Polyploid plants comprised 90% of all specimens and their proportion ranged between 0% and 100% per site. However, this proportion was not correlated with aridity along the large-scale gradient, nor were polyploids more frequently found on Southern exposures.

Our results show for both spatial scales that increasing aridity is not the principal driver for the distribution of polyploids in B. distachyon s.l. in Israel. Notably, though, diploid plants were restricted essentially to four intermediate sites, while polyploids dominated the most arid and the most mesic sites. This, to some degree, clustered pattern suggests that the distribution of cytotypes is not entirely random and calls for future studies to assess further potential drivers.