Molekularna osnova auto-inkompatibilnog sistema heljde (Fagopyrum esculentum Moench)

Abstract

Heljda (fam. Polygonaceae) je heteromorfna biljna vrsta koja sadrži cvetove dve morfologije: "pin" (dugačak stubić tučka, kratke antere, manja polenova zrna) i "tram" (kratak stubić tučka, dugačke antere, veća polenova zrna). Oplođenje je dozvoljeno samo između cvetova različite morfologije, dok je sprečeno između cvetova iste morfologije delovanjem sistema auto-inkompatibilnosti (AI), koji ne dozvoljava ukrštanje u srodstvu. Heljda se zbog svojih dobrih nutritivnih osobina gaji širom sveta, a osnovni problem u njenom uzgajanju predstavljaju nizak i nepouzdan prinos i visoka otpornost na introgresiju novih osobina iz srodnih vrsta, što su direktne posledice njene AI. Ovakvo delovanje AI sistema može predstavljati prepreku u uzgajanju i oplemenjivanju poljoprivredno značajnih vrsta (npr. badem, heljda, itd.), odatle i veliki interes za proučavanje ovih sistema. Kroz njihovo upoznavanje može se omogućiti proizvodnja samooplodnih i hibridnih linija željenih svojstava, kao i razvijanje novih markera, pomoću kojih se ubrzava proces selekcije, što bi dovelo do povećanja prinosa uz snižavanje troškova gajenja. Ono što je poznato o heljdinom AI odgovoru jeste da predstavlja genetički determinisanu kaskadu biohemijskih reakcija, koja dovodi do zaustavljanja rasta polenove cevi ako je polen prepoznat kao sopstveni. Rast sopstvene polenove cevi se zaustavlja na spoju žiga i stubića "tram" tučka, odnosno na 2/3 dužine stubića "pin" tučka. Ova reakcija je pod kontrolom Ssupergena, koji pored AI gena sadrži i gene koji određuju dužinu stubića tučka, visinu antera i veličinu polenovog zrna, koji se zajedno vezano nasleđuju. Između alela AI gena postoji dominantno-recesivan odnos, u kom su "pin" biljke recesivni homozigoti za AI gen, ss, dok su "tram" biljke dominantni heterozigoti, Ss. Pošto se pri oplođenju "tram" polen ponaša u skladu sa diploidnim genotipom roditeljske biljke, a ne sopstvenim haploidnim genotipom, zaključeno je da kod heljde postoji sporofitna determinacija AI. Poslednjih godina razvijeni su molekularni markeri za fino mapiranje S-lokusa heljde, a sekvenciran je i transkriptom cveta heljde, što omogućuje detekciju novih S-sekvenci. Identifikovan je i prvi kandidat gena S-lokusa heljde, gen S-ELF3, koji najverovatnije određuje "tram" fenotip tučka...

Buckwheat (fam. Polygonaceae) is heteromorphic species with two flower morphs: "pin" (long style, short anthers, and smaller pollen grains) and "thrum" (short style, long anthers, and larger pollen grains). Fertilization is allowed only between flowers of different morphology, while it is prevented between flowers of the same morphology, trough selfincompatibility (SI) system, which prevents inbreeding. Buckwheat is grown worldwide due to its good nutritive characteristics, but the main issue in its breeding is low and uncertain yield and high resistance of buckwheat to introgression of new characteristics from related wild species, all of which are direct cosequences of buckwheat's SI. These effects of SI systems may present obstacles in breeding of agriculturally important species (i.e. almond, buckwheat, etc.), hence the interest in SI system studies. The aim of SI systems studies is to provide self-fertile and hybrid lines of desired characteristics, as well as to provide new markers for marker-assisted selections, all of which would improve the yield, while lowering the costs of breeding. Current understanding of buckwheat SI system considers SI response as genetically determined cascade of biochemical reactions that lead to pollen tube arrest when pollen has been recognized as self. The site of self-pollen tube arrest is different in two morphs: in "thrum" morph it occurs at the stigma-style junction, while in "pin" it takes place at 2/3 of style’s length. This reaction is under the control of the S-supergene which comprises SI genes and closely linked genes that determine style’s length, anthers’ height and pollen grain size, inherited as a single unit. Between SI alleles there is a dominant-recessive relationship, in which “pin” plants act as recessive homozygotes, ss, while “thrum” plants act as dominant heterozygotes, Ss. Since “thrum” pollen behaves in accordance with a diploid genotype of its parental plant and not its own haploid genotype, it was concluded that SI in buckwheat is sporophytically determined. Recently, molecular markers for fine mapping of S-locus were developed, and flower transcriptome was sequenced, which enables detection of new S-sequences. First buckwheat S-gene was identified as S-ELF3 gene, which is the most probable candidate for the "thrum" pistil phenotype determinant.