Low temperature-induced necrosis shows phenotypic plasticity in wheat triploid hybrids

Abstract

Common wheat (Triticum aestivum L.) is an allohexaploid species (AABBDD genome), derived through endoreduplication of an interspecific triploid hybrid between cultivated tetraploid wheat Triticum turgidum L. (AABB genome) and a wild diploid relative, Aegilops tauschii Coss (DD genome). Natural hybridization of the parental species, avoidance of hybrid breakdown, and formation of unreduced gametes are essential for hexaploidization. 1The breakdown of wheat triploid hybrids was first reported in Nishikawa's pioneer works.2-4 It was recently found that cultivar Langdon of T. turgidum subspecies durum is an efficient AB genome parent for production of hexaploid wheat synthetics, 5 allowing us to produce a number of synthetic hexaploid wheat lines with D genomes derived from various accessions of Ae. tauschii. 6,7 In the process of synthetic wheat production, we found several types of hybrid abnormalities including hybrid necrosis and hybrid chlorosis, 8,9 as Nishikawa reported previously in references 2-4.Hybrid necrosis is one of the post-zygotic hybridization barriers between two diverging lineages within the same species or in two closely related species. 10 The Dobzhansky-Muller model simply explains the process for generating hybridization barriers. 11,12 In diploid species, post-zygotic hybridization barriers, including hybrid necrosis, function in a positive manner to accelerate establishment of a new diploid species. Recent reports showed that the causal genes for hybrid necrosis are defense response-related genes in higher plants such as Arabidopsis and lettuce. [13][14][15][16] These hybrid necrosis genes act to accelerate genetic differentiation among genetically related accessions in the same species and between hybrid necrosis sometimes appears in triploid hybrids between tetraploid wheat and Aegilops tauschii Coss. two types of hybrid necrosis (type ii and type iii) were observed when cultivar Langdon was used as female parent for hybrid production. type ii necrosis symptoms occurred only under low temperature conditions, whereas bushy and dwarf phenotypes were observed under normal temperature conditions. the developmental plasticity might be related to a temperature-responsive alteration of meristematic activity at the crown tissue of triploid hybrids. Epistatic interaction between the aB and D genomes induced not only upregulation of a number of defense-related genes, but also extensive changes in plant architecture in the type ii necrosis hybrids. Such phenotypic plasticity was also observed in other cross combinations between cultivated tetraploid wheat and type ii necrosis-induced Ae. tauschii accessions. Wild tetraploid wheat, Triticum turgidum subspecies dicoccoides, did not induce type ii necrosis in the triploid hybrids, indicating the possibility of identifying the chromosomal location of a causal gene for type ii necrosis in the aB genome. Low temperature-induced necrosis shows phenotypic plasticity in wheat triploid hybridsShigeo takumi* and nobuyuki mizuno Graduate School of agricultura...

Comparison of gene expression profiles and responses to zinc chloride among inter- and intraspecific hybrids with growth abnormalities in wheat and its relatives

“…5). Necrotic cell death requires low-temperature conditions, and normal growth temperatures such as 23 °C cannot induce any necrotic symptoms in plants showing type II necrosis Takumi and Mizuno 2011). Low-temperature treatment activates a number of wheat cold-responsive genes, resulting in differences in gene expression profiles for plants showing type II necrosis from profiles seen for other growth incompatibilities.…”

Hybrid incompatibilities in interspecific crosses between tetraploid wheat and its wild diploid relative Aegilops umbellulata

“…In ABD F1 hybrids and Ldn/Ae. tauschii synthetic hexaploid lines, grass-clump dwarfism is dramatically affected by growth temperature, and under the low temperature condition, the growth phenotype changes from grass-clump dwarf to type II necrosis with repression of stem elongation and delayed new-leaf expansion (Mizuno et al 2011;Takumi and Mizuno 2011).…”

“…In type II hybrid necrosis, necrotic cell death occurs only under low temperature conditions (Mizuno et al 2011). At normal growth temperatures, hybrids with type II necrosis exhibit grass-clump dwarfism with no necrotic symptoms, but with excess tillers, severe dwarfism and delayed flowering (Takumi and Mizuno 2011;Matsuda et al 2017).…”

Global gene expression profiling related to temperature-sensitive growth abnormalities in interspecific crosses between tetraploid wheat and Aegilops tauschii

“…The type II necrosis lines exhibit a significant decrease in expression of genes related to the cell cycle and cell division occurs at the crown tissues including the shoot apical meristem [ 14 ]. Interestingly, the ABD triploids with type II necrosis show dramatic increase in tiller number and marked reduction of plant height at normal temperature [ 14 , 18 ]. No necrotic symptoms are observed and the start of senescence seemed to be delayed in the type II necrosis lines under normal temperature, and heading and flowering are remarkably delayed (by more than 3 weeks) in the type II necrosis plants compared with those in other synthetics with a normal phenotype under glasshouse conditions [ 18 ].…”