The changes in the reproductive barrier between hexaploid wheat (Triticum aestivum L.) and rye (Secale cereale L.): different states lead to different fates

Abstract

The changes in the reproductive barrier between hexaploid wheat ( Triticum aestivum L.) and rye ( Secale cereale L.) can be induced using in situ embryo rescue of abnormal embryos, yielding stable fertile amphidiploid plants. In intergeneric crosses between hexaploid wheat (Triticum aestivum L.) and rye (Secale cereale L.), postzygotic barriers may occur at different stages of hybrid development. One such mechanism is embryo lethality, which is genetically determined by the interaction and expression of two incompatible genes in wheat (Eml-A1) and rye (Eml-R1). Using in vitro culture methods as stressors, we overcame this hybrid lethality. Normal and abnormal embryos were observed to build embryogenic calli and produce regenerated plantlets in a similar manner. The high regenerative capacity of the abnormal embryos led us to conclude that the reproductive barrier in these intergeneric hybrids may have an epigenetic origin that can be easily overcome by culturing immature embryos via callus induction. After colchicine treatment during callus culture, amphidiploid plants were obtained. However, most of these plants did not produce seeds, due mainly to sterility of the pollen but also of the embryo sacs. These findings demonstrate that hybrid sterility affects both male and female gametophytes in plants obtained from abnormal embryos. The key roles of double fertilization and stress factors in the implementation of the apical meristem formation program in embryos from incompatible intergeneric crosses between hexaploid wheat and rye during in vitro culture are discussed. We also propose a hypothetical model for a wheat-rye lethality system involving differential expression of incompatible wheat Eml-A1 and rye Eml-R1b alleles in an identical genetic background.

Major chromosome rearrangements in intergeneric wheat × rye hybrids in compatible and incompatible crosses detected by GBS read coverage analysis

“…These plants were labeled with the number of GBS probe. From the incompatible cross (CS × L2), 229 amphidiploid plants (ADL2, R 0 ) were obtained by in vitro embryo rescue, but only eight plants produced seeds 13 . The descendants of these eight ADL2 plants of R 0 , R 1 –R 3 generations were cultivated under greenhouse and field conditions (Table 1 ).…”

“…To obtain hybrids, wheat spikes were emasculated 1–2 days before anthesis and pollinated 2–4 days later with fresh rye pollen. Hybrid embryos were excised 14 or 16 days after pollination (DAP), sterilized and cultivated, as reported by Tikhenko et al 13 . Chromosome doubling was performed by in vitro colchicine application as described by Sood et al 24 with some modifications 13 .…”

“…However, not every combination of tetraploid or hexaploid wheat with rye results in a viable hybrid 2 , 9 , 10 . To overcome both prezygotic 11 , 12 and postzygotic 13 reproductive barriers between wheat and rye, different methods are being developed, including the transfer of recessive crossability alleles kr1 , kr2, skr into well-adapted wheat varieties and in situ embryo rescue of abnormal embryos, yielding fertile amphidiploid plants. Furthermore, to optimize pre-breeding programs for triticale, it is necessary to develop effective methods for obtaining viable offspring 2 , 6 , 10 and study the mechanisms of genome restructuring and ways to stabilize the new complex hybrid genome 14 – 17 .…”

Standardization of Regeneration Protocol in Wheat-Rye Crosses from Immature Embryos

“…Neverthless, Raghavan (1980) felt that hormones might have a profound influence on embryo development. Tikhenko et al, (2017) reported that the changes in the reproductive barrier between hexaploid wheat and rye could be induced using in situ embryo rescue of abnormal embryos, yielding stable fertile amphidiploid plants.…”

Leaf chlorosis in Arabidopsis thaliana hybrids is associated with transgenerational decline and imbalanced ribosome number

“…The majority of genes causing hybrid incompatibilities reported so far are dominant, but incompatibilities can also be due to recessive genes and only become visible in the F 2 or later generations. This phenomenon, known as hybrid breakdown, is common in many plant species including Arabidopsis, rice, wheat and rye (Mizuta et al , 2010; Matsubara et al , 2014; Okada et al , 2017; Tikhenko et al , 2017; Alhajturki et al , 2018). According to the Bateson–Dobzhansky–Muller (BDM) model, hybrid incompatibility could occur between two interacting genes that evolve independently in the parental populations.…”