*Article* **Transgenerational Paternal Inheritance of** *TaCKX* **GFMs Expression Patterns Indicate a Way to Select Wheat Lines with Better Parameters for Yield-Related Traits**

**Karolina Szala , Marta Dmochowska-Boguta , Joanna Bocian , Waclaw Orczyk and Anna Nadolska-Orczyk \***

> Department of Functional Genomics, Plant Breeding and Acclimatization Institute—National Research Institute, Radzikow, 05-870 Blonie, Poland

**\*** Correspondence: a.orczyk@ihar.edu.pl

**Abstract:** Members of the *TaCKX* gene family (GFMs) encode the cytokinin oxygenase/dehydrogenase enzyme (CKX), which irreversibly degrades cytokinins in the organs of wheat plants; therefore, these genes perform a key role in the regulation of yield-related traits. The purpose of the investigation was to determine how expression patterns of these genes, together with the transcription factor-encoding gene *TaNAC2-5A*, and yield-related traits are inherited to apply this knowledge to speed up breeding processes. The traits were tested in 7 days after pollination (DAP) spikes and seedling roots of maternal and paternal parents and their F<sup>2</sup> progeny. The expression levels of most of them and the yield were inherited in F<sup>2</sup> from the paternal parent. Some pairs or groups of genes cooperated, and some showed opposite functions. Models of up- or down-regulation of *TaCKX* GFMs and *TaNAC2-5A* in low-yielding maternal plants crossed with higher-yielding paternal plants and their high-yielding F<sup>2</sup> progeny reproduced gene expression and yield of the paternal parent. The correlation coefficients between *TaCKX* GFMs, *TaNAC2-5A*, and yield-related traits in high-yielding F<sup>2</sup> progeny indicated which of these genes were specifically correlated with individual yield-related traits. The most common was expressed in 7 DAP spikes *TaCKX2.1*, which positively correlated with grain number, grain yield, spike number, and spike length, and seedling root mass. The expression levels of *TaCKX1* or *TaNAC2-5A* in the seedling roots were negatively correlated with these traits. In contrast, the thousand grain weight (TGW) was negatively regulated by *TaCKX2.2.2*, *TaCKX2.1*, and *TaCKX10* in 7 DAP spikes but positively correlated with *TaCKX10* and *TaNAC2-5A* in seedling roots. Transmission of *TaCKX* GFMs and *TaNAC2-5A* expression patterns and yield-related traits from parents to the F<sup>2</sup> generation indicate their paternal imprinting. These newly shown data of nonmendelian epigenetic inheritance shed new light on crossing strategies to obtain a high-yielding F<sup>2</sup> generation.

**Keywords:** parental imprinting; transgenerational epigenetics; paternal inheritance; wheat; *TaCKX* expression; cytokinin; yield
