High grain yield is a key desirable trait in cereal crops. Floret fertility
determines the number of grains per inflorescence (referred to as spike) of
cereals such as bread wheat or barley. However, little was known about its
genetic basis.

A group of researchers from Japan, Germany, and Israel have now collaborated
to decode the genetic basis of floret infertility in wheat. The group
focused on the quantitative trait loci (QTL) responsible for enhanced grain
number per spikelet, which was previously identified by a genomewide
association analysis of European winter bread wheat. They mapped the QTL and
identified the gene Grain Number Increase 1 (GNI-A1), which evolved in the
Triticeae tribe through gene duplication, on chromosome arm 2AL.

The scientists showed that the resulting GNI-A1 encoded a homeodomain
leucine zipper class I (HD-Zip I) transcription factor, which inhibited the
growth and development of wheat florets within the spikelets. In the
domestication process, a decrease of GNI1 expression led to more fertile
florets and an increase in grains per spikelet. However, additional analysis
of high-yielding bread wheat cultivars revealed a reduced-function allele of
the GNI-A1 gene. This mutated allele was found in modern wheat with higher
floret fertility. This implies that the mutated allele increased floret
fertility and that a selection for wheat cultivars carrying the
reduced-function allele had taken place during further wheat-domestication.

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