Identification and Molecular Analysis of Putative Self-Incompatibility Ribonuclease Alleles in an Extreme Polyploid Species, Prunus laurocerasus L

Cherry laurel (Prunus laurocerasus L.) is an extreme polyploid (2n = 22x) species of the Rosaceae family where gametophytic self-incompatibility (GSI) prevents inbreeding. This study was carried out to identify the S-ribonuclease alleles (S-RNases) of P. laurocerasus using PCR amplification of the first and second intron region of the S-RNase gene, cloning and sequencing. A total of 23 putative S-RNase alleles (S ₁-S ₂₀, S _{5 m}, S _{13 m}, and S _{18 m}) were sequenced from the second (C2) to the fifth conserved region (C5), and they shared significant homology to other Prunus S-RNases. The length of the sequenced amplicons ranged from 505 to 1,544 bp, and similar sizes prevented the proper discrimination of some alleles based on PCR analysis. We have found three putatively non-functional alleles (S _{5 m}, S _{18 m}, and S ₉) coding for truncated proteins. Although firm conclusions cannot be drawn, our data seem to support that heteroallelic pollen cannot induce self-compatibility in this polyploid Prunus species. The identities in the deduced amino acid sequences between the P. laurocerasus and other Prunus S-RNases ranged between 44 and 100%, without a discontinuity gap separating the identity percentages of trans-specific and more distantly related alleles. The phylogenetic position, the identities in nucleotide sequences of the second intron and in deduced amino acid sequences found one or more trans-specific alleles for all but S ₁₀, S ₁₄, S ₁₈, and S ₂₀ cherry laurel RNases. The analysis of mutational frequencies in trans-specific allele pairs indicated the region RC4-C5 accepts the most amino acid replacements and hence it may contribute to allele-specificity. Our results form the basis of future studies to confirm the existence and function of the GSI system in this extreme polyploid species and the alleles identified will be also useful for phylogenetic studies of Prunus S-RNases as the number of S-RNase sequences was limited in the Racemose group of Prunus (where P. laurocerasus belongs to).

Interaction between elevated temperature and different types of Na-salicylate treatment in Brachypodium dystachion

Salicylic acid (SA) plays a role in several physiological processes in plants. Exogenously applied SA is a promising tool to reduce stress sensitivity. However, the mode of action may depend on how the treatment was performed and environmental conditions may alter the effects of SA. In the present study the physiological and biochemical effects of different modes of application (soaking seeds prior sowing; spraying leaves with 0.5 mM NaSA) were compared at normal and moderately elevated temperatures (4 h; 35°C) in Brachypodium distachyon (L.) P. Beauv. plants. While soaking the seeds stimulated plant growth, spraying caused mild stress, as indicated by the chlorophyll-a fluorescence induction parameters and changes in certain protective compounds, such as glutathione, flavonoids or antioxidant enzymes. Elevated temperature also caused an increase in the glutathione-S-transferase activity, and this increase was more pronounced in plants pre-treated with NaSA. Both seed soaking or spraying with NaSA and exposure to heat treatment at 35°C reduced the abscisic acid levels in the leaves. In contrast to abscisic acid, the jasmonic acid level in the leaves were increased by both spraying and heat treatment. The present results suggest that different modes of application may induce different physiological processes, after which plants respond differently to heat treatment. Since these results were obtained with a model plants, further experiments are required to clarify how these changes occur in crop plants, especially in cereals.