Cytoplasm of the Wild Species Aegilops mutica Reduces VRN1 Gene Expression in Early Growth of Cultivated Wheat: Prospects for Using Alloplasmic Lines to Breed Varieties Adapted to Global Warming

In a warm winter due to climate warming, it is necessary to suppress early flowering of autumn-sown wheat plants. Here, we propose the use of cytoplasmic genome effects for this purpose. Alloplasmic lines, or cytoplasmic substitution lines, of bread wheat (<i>Triticum aestivum</i>) have cytoplasm from a related wild <i>Aegilops</i> species through recurrent backcrossing and exhibit altered characteristics compared with the euplasmic lines from which they are derived. Thus, alloplasmic lines with <i>Aegilops mutica</i> cytoplasm show delayed flowering compared with lines carrying normal cytoplasm. In the wheat flowering pathway, <i>VERNALIZATION 1</i> (<i>VRN1</i>) encodes an APETALA1/FRUITFULL-like MADS box transcription factor that plays a central role in the activation of florigen genes, which induce floral meristems in the shoot apex. Here, we compared expression of <i>VRN1</i> alleles in alloplasmic and euplasmic lines after vernalization. We found that alloplasmic wheat showed a lower level of <i>VRN1</i> expression after vernalization compared with euplasmic wheat. Thus, nuclear-cytoplasm interactions affect the expression levels of the nuclear <i>VRN1</i> gene; these interactions might occur through the pathway termed retrograde signaling. In warm winters, autumn-sown wheat cultivars with spring habit can pass through the reproductive growth phase in very early spring, resulting in a decreased tiller/ear number and reduced yield performance. Here, we present data showing that an alloplasmic line of 'Fukusayaka' can avoid the decrease in tiller/ear numbers during warm winters, suggesting that this alloplasmic line may be useful for development of varieties adapted to global warming.