During the initial step of the symbiosis between legumes (Fabaceae) and nitrogen-fixing bacteria (rhizobia), the bacterial signal molecule known as the Nod factor (nodulation factor) is recognized by plant LysM motif-containing receptor-like kinases (LysM-RLKs). The fifth chromosome of barrel medic (Medicago truncatula Gaertn.) contains a cluster of paralogous LysM-RLK genes, one of which is known to participate in symbiosis. In the syntenic region of the pea (Pisum sativum L.) genome, three genes have been identified: PsK1 and PsSym37, two symbiosis-related LysM-RLK genes with known sequences, and the unsequenced PsSym2 gene which presumably encodes a LysM-RLK and is associated with increased selectivity to certain Nod factors. In this work, we identified a new gene encoding a LysM-RLK, designated as PsLykX, within the Sym2 genomic region. We sequenced the first exons (corresponding to the protein receptor domain) of PsSym37, PsK1, and PsLykX from a large set of pea genotypes of diverse origin. The nucleotide diversity of these fragments was estimated and groups of haplotypes for each gene were revealed. Footprints of selection pressure were detected via comparative analyses of SNP distribution across the first exons of these genes and their homologs MtLYK2, MtLYK3, and MtLYK4 from M. truncatula retrieved from the Medicago Hapmap project. Despite the remarkable similarity among all the studied genes, they exhibited contrasting selection signatures, possibly pointing to diversification of their functions. Signatures of balancing selection were found in LysM1-encoding parts of PsSym37 and PsK1, suggesting that the diversity of these parts may be important for pea LysM-RLKs. The first exons of PsSym37 and PsK1 displayed signatures of purifying selection, as well as MtLYK2 of M. truncatula. Evidence of positive selection affecting primarily LysM domains was found in all three investigated M. truncatula genes, as well as in the pea gene PsLykX. The data suggested that PsLykX is a promising candidate for PsSym2, which has remained elusive for more than 30 years.

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Arbuscular mycorrhiza (AM) is known to be a mutually beneficial plant-fungal symbiosis; however, the effect of mycorrhization is heavily dependent on multiple biotic and abiotic factors. Therefore, for the proper employment of such plant-fungal symbiotic systems in agriculture, a detailed understanding of the molecular basis of the plant developmental response to mycorrhization is needed. The aim of this work was to uncover the physiological and metabolic alterations in pea (Pisum sativum L.) leaves associated with mycorrhization at key plant developmental stages. Plants of pea cv. Finale were grown in constant environmental conditions under phosphate deficiency. The plants were analyzed at six distinct time points, which corresponded to certain developmental stages of the pea: I: 7 days post inoculation (DPI) when the second leaf is fully unfolded with one pair of leaflets and a simple tendril; II: 21 DPI at first leaf with two pairs of leaflets and a complex tendril; III: 32 DPI when the floral bud is enclosed; IV: 42 DPI at the first open flower; V: 56 DPI when the pod is filled with green seeds; and VI: 90–110 DPI at the dry harvest stage. Inoculation with Rhizophagus irregularis had no effect on the fresh or dry shoot weight, the leaf photochemical activity, accumulation of chlorophyll a, b or carotenoids. However, at stage III (corresponding to the most active phase of mycorrhiza development), the number of internodes between cotyledons and the youngest completely developed leaf was lower in the inoculated plants than in those without inoculation. Moreover, inoculation extended the vegetation period of the host plants, and resulted in increase of the average dry weight per seed at stage VI. The leaf metabolome, as analyzed with GC-MS, included about three hundred distinct metabolites and showed a strong correlation with plant age, and, to a lesser extent, was influenced by mycorrhization. Metabolic shifts influenced the levels of sugars, amino acids and other intermediates of nitrogen and phosphorus metabolism. The use of unsupervised dimension reduction methods showed that (i) at stage II, the metabolite spectra of inoculated plants were similar to those of the control, and (ii) at stages IV and V, the leaf metabolic profiles of inoculated plants shifted towards the profiles of the control plants at earlier developmental stages. At stage IV the inoculated plants exhibited a higher level of metabolism of nitrogen, organic acids, and lipophilic compounds in comparison to control plants. Thus, mycorrhization led to the retardation of plant development, which was also associated with higher seed biomass accumulation in plants with an extended vegetation period. The symbiotic crosstalk between host plant and AM fungi leads to alterations in several biochemical pathways the details of which need to be elucidated in further studies.

ВВЕДЕНИЕÇíà÷èòåëüíîå óâåëè÷åíèå èñïîëüçîâàíèÿ àãðîõèìèêàòîâ â ïåðèîä ñ 1960 ãîäà ïî 2000 ãîä â ðåçóëüòàòå èíòåíñèôèêàöèè ñåëüñêîõîçÿé-ñòâåííîãî ïðîèçâîäñòâà ïðèâåëî ê çíà÷èòåëüíîìó èñòîùåíèþ åñòå-ñòâåííîãî ïîòåíöèàëà ïëîäîðîäèÿ ïî÷â, óõóäøåíèþ êà÷åñòâà âîäû è âîçäóõà, ñíèaeåíèþ êà÷åñòâà îïðåäåëåííûõ âèäîâ ñåëüñêîõîçÿéñòâåí-íîé ïðîäóêöèè [23].  ñâÿçè ñ ýòèì â íàñòîÿùåå âðåìÿ íàáëþäàåòñÿ èçìåíåíèå îñíîâíîé êîíöåïöèè ñåëüñêîãî õîçÿéñòâà îò èíòåíñèâíîãî ê óñòîé÷èâîìó, ýêîëîãè÷åñêè-îðèåíòèðîâàííîìó. Îäíèì èç ïåðñïåê-òèâíûõ íàïðàâëåíèé ñîâðåìåííîãî çåìëåäåëèÿ ÿâëÿåòñÿ èñïîëüçîâà-íèå ïîòåíöèàëà ïîëåçíîé ïî÷âåííîé ìèêðîôëîðû. Ñèìáèîòè÷åñêèå ìèêðîîðãàíèçìû èãðàþò âàaeíóþ ðîëü â ðàçâèòèè ðàñòåíèé, îáåñïå-÷èâàÿ èõ ìèíåðàëüíîå ïèòàíèå, çàùèòó îò ïàòîãåíîâ è âðåäèòåëåé, àäàïòàöèþ ê ðàçëè÷íûì ñòðåññàì [8,9].Íàèáîëåå âàaeíîå ýêîëîãè÷åñêîå è ïðàêòè÷åñêîå çíà÷åíèå èìåþò ýíäîñèìáèîòè÷åñêèå ñèñòåìû: áîáîâî-ðèçîáèàëüíûé ñèìáèîç è àð-áóñêóëÿðíàÿ ìèêîðèçà (ÀÌ). Ñèìáèîç ñ êëóáåíüêîâûìè áàêòåðèÿìè (ÊÁ) ðîäîâ Rhizobium, Sinorhizobium, Bradyrhizobium è äð. ïîçâîëÿåò áîáîâûì ðàñòåíèÿì ðàçâèâàòüñÿ â óñëîâèÿõ äåôèöèòà ñâÿçàííîãî àçîòà, òîãäà êàê âçàèìîäåéñòâèå ñ ÀÌ ãðèáàìè, ôèëà Glomeromycota [21], îáåñïå÷èâàåò àññèìèëÿöèþ òðóäíîðàñòâîðèìûõ ôîñôàòîâ è äðóãèõ ïèòàòåëüíûõ ýëåìåíòîâ ïî÷âû. Èíîêóëÿöèÿ áîáîâûõ êóëüòóð ÊÁ ïðèâîäèò ê ñóùåñòâåííîìó óâåëè÷åíèþ óðîaeàÿ (îò 15 % äî 60 %), à òàêaeå ê ôèêñàöèè 40-450 êã àçîòà íà ãåêòàð çà ñåçîí [11]. Ðåçóëü-òàòîì øèðîêîãî ïðèìåíåíèÿ áèîïðåïàðàòîâ íà îñíîâå ÊÁ ÿâëÿåòñÿ ñíèaeåíèå ïðèìåíåíèÿ àçîòíûõ óäîáðåíèé è àêêóìóëÿöèè íèòðàòîâ ðàñòåíèÿìè, ïî÷âîé è âîäîé. Ìèêîðèçàöèÿ âåäåò ê óëó÷øåíèþ ðîñòà ðàñòåíèé, îäíàêî øèðîêîå èñïîëüçîâàíèå ýòîãî ñèìáèîçà îãðàíè÷åíî ñëîaeíîñòüþ ïðèãîòîâëåíèÿ ïðåïàðàòîâ ìèêîðèçíûõ ãðèáîâ. Áîáî-âî-ðèçîáèàëüíûé è ÀÌ ñèìáèîçû òàêaeå ïðåäîõðàíÿþò ïî÷âû îò èñòîùåíèÿ è ïîääåðaeèâàþò áèîëîãè÷åñêîå ðàçíîîáðàçèå ðàñòèòåëü-íûõ ñîîáùåñòâ [12,16]. Ýòè äâà ñèìáèîçà ñèëüíî ðàçëè÷àþòñÿ ïî ôèçèîëîãèè, ìîðôîëîãèè è ñïåöèôè÷íîñòè âçàèìîäåéñòâèÿ. Òåì íå ìåíåå ó áîáîâûõ ðàñòåíèé âûÿâëåíà åäèíàÿ ñèñòåìà ðàçâèòèÿ ýòèõ ñèìáèîçîâ, êîòîðàÿ èìååò ìíîãî îáùèõ ýëåìåíòîâ ñ ñèñòåìàìè çàùè-òû ðàñòåíèé îò ïàòîãåíîâ è ÿâëÿåòñÿ îñíîâîé ðàñòèòåëüíî-ìèêðîáíî-ãî ýâîëþöèîííîãî êîíòèíóóìà [8,9]. Îäíàêî â ëèòåðàòóðå îïèñàíî