YABBY genes are plant-specific transcription factors (TF) that function in plant growth and development.  To investigate the functions of the YABBY genes in plants’ stress tolerance, we analyzed the YABBY genes in foxtail millet (Setaria italica) and investigated their functions on plant growth and responses to different stresses.  Eight YABBY genes were identified on five chromosomes. These genes showed strong relationships with YABBY genes in other monocot species.  Phylogenetical SiYABs were classified into four clades: FIL/YAB3, YAB2, INO, and CRC.  No monocot YABBY member was classified into the YAB5 clade.  Four conserved motifs were identified and motif 1 constituted the YABBY domain, whereas motifs 2 and 3 formed the C2-C2 region. SiYAB genes were highly expressed in reproductive tissues.  Among all the SiYABs, SiDL was selected to be overexpressed in Arabidopsis thaliana to check the functions of the YABBY genes.  Overexpression of SiDL in Arabidopsis thaliana caused delayed flowering, leaf curling, and reduced seed size.  In addition, SiDL acted as a negative regulator in plant response to salt stress. Our study provides information to assist the study of YABBY gene function in S. italica.

Foxtail millet (Setaria italica L.) is an important food and fodder crop in semi-arid areas.  However, there are few herbicides suitable for use on weed control in field-grown foxtail millet during the post-emergence herbicides stage.  The present study was conducted using four concentrations (0.5, 1, 2, and 4 L ai ha^–1) of foliar-applied fluroxypyr, and the effect of fluroxypyr on selected metabolic and stress-related parameters in foxtail millet were assessed after 15 days.  In this study, increasing concentrations decreased plant height and accumulation of chlorophylls.  Our results also showed that malondialdehyde (MDA) accumulated in response to fluroxypyr application, demonstrating increased lipid peroxidation due to excessive reactive oxygen species production.  In response to this oxidative stress, the activities of antioxidant enzymes were generally enhanced.  Non-enzymatic antioxidant defense systems, which function in concert with antioxidant enzymes, can also protect plant cells from oxidative damage by scavenging reactive oxygen species (ROS).  In conclusion, the hybrid variety (Zhangzagu) exhibited a greater tolerance to fluroxypyr than did the conventional variety Jingu 21, which might be associated with the antioxidant mechanisms of Zhangzagu hybrid millet.