The interaction of plants with certain types of parasites leads to the formation of galls, organised structures that create the habitat of the parasite, caused by an abnormal proliferation of host plant's cells under the influence of growth regulators, secreted by the parasite, or by the plant itself under the influence of the parasite. Arthropods, mites in particular, are the largest group of gall-inducing phytoparasites, but the mechanisms of their interaction with plants remain virtually unexplored. The interaction of the gall-inducing eriophyoid mite Fragariocoptes setiger with Fragaria viridis plants was used as a model gall-mite system where data were obtained on the changes in the histological structure of F. viridis leaf blades under the influence of the mites as well as F. viridis gene expression during gall formation. For histological purposes, gall formation was split into four stages with each corresponding to the age of the gall as well as to specific changes that occur during that period. A dramatic change of adaxial-abaxial polarity of the lamina throughout the four stages was observed. Moreover, qRT-PCR analysis of F. viridis gene expression in the developing gall revealed changes in the expression levels of certain meristem-specific genes, as well as the genes that determine adaxial-abaxial polarity and signalling of phytohormones. Petersburg State University and the resource centre of the Komarov Botanical Institute of RAS.

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Developing seeds of some higher plants are photosynthetically active and contain chlorophylls (Chl), which are typically destroyed at the late stages of seed maturation. However, in some crop plant cultivars, degradation of embryonic Chl remains incomplete, and mature seeds preserve green colour, as it is known for green-seeded cultivars of pea (Pisum sativum L.). The residual Chl compromise seed quality and represent a severe challenge for farmers. Hence, comprehensive understanding of the molecular mechanisms, underlying incomplete Chl degradation is required for maintaining sustainable agriculture. Therefore, here we address dynamics of plastid conversion and photochemical activity alterations, accompanying degradation of Chl in embryos of yellow- and green-seeded cultivars Frisson and Rondo respectively. The yellow-seeded cultivar demonstrated higher rate of Chl degradation at later maturation stage, accompanied with termination of photochemical activity, seed dehydration and conversion of green plastids into amyloplasts. In agreement with this, expression of genes encoding enzymes of Chl degradation was lower in the green seeded cultivar, with the major differences in the levels of Chl b reductase (NYC1) and pheophytinase (PPH) transcripts. Thus, the difference between yellow and green seeds can be attributed to incomplete Chl degradation in the latter at the end of maturation period.

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