Temporal dynamics of N-hydroxypipecolic acid and salicylic acid pathways in the disease response to powdery mildew in wheat.

Wheat (Triticum aestivum) is a major staple crop worldwide, and its yields are significantly threatened by wheat powdery mildew (Blumeria graminis f. sp. tritici). Enhancing disease resistance in wheat is crucial for meeting global food demand. This study investigated the disease response in wheat, focusing on the bioactive small molecules salicylic acid (SA), pipecolic acid (Pip), and N-hydroxypipecolic acid (NHP), to provide new insights for molecular breeding. We found that endogenous levels of SA, Pip, and NHP significantly increased in infected plants, with Pip and NHP levels rising earlier than those of SA. Notably, the rate of increase of NHP was substantially higher than that of SA. The gene expression levels of SARD1 and CBP60g, which are transcription factors for SA, Pip, and NHP biosynthesis, increased significantly during the early stages of infection. We also found that during the later stages of infection, the expression of ALD1, SARD4, and FMO1, which encode enzymes for Pip and NHP biosynthesis, dramatically increased. Additionally, ICS1, which encodes a key enzyme involved in SA biosynthesis, also showed increased expression during the later stages of infection. The temporal changes in ICS1 transcription closely mirrored the behavior of endogenous SA levels, suggesting that the ICS pathway is the primary route for SA biosynthesis in wheat. In conclusion, our results suggest that the early accumulation of Pip and NHP cooperates with SA in the disease response against wheat powdery mildew infection.

Metabolic profiles in drought-tolerant wheat with enhanced abscisic acid sensitivity.

Global warming has led to the expansion of arid lands and more frequent droughts, which are the largest cause of global food production losses. In our previous study, we developed TaPYLox wheat overexpressing the plant hormone abscisic acid (ABA) receptor, which is important for the drought stress response in plants. TaPYLox showed resistance to drought stress and acquired water-saving traits that enable efficient grain production with less water use. In this study, we used TaPYLox to identify ABA-dependent and -independent metabolites in response to drought stress. We compared the variation of metabolites in wheat under well-watered, ABA treatment, and drought stress conditions using the ABA-sensitive TaPYLox line and control lines. The results showed that tagatose and L-serine were ABA-dependently regulated metabolites, because their stress-induced accumulation was increased by ABA treatment in TaPYLox. In contrast, L-valine, L-leucine, and DL-isoleucine, which are classified as branched chain amino acids, were not increased by ABA treatment in TaPYLox, suggesting that they are metabolites regulated in an ABA-independent manner. Interestingly, the accumulation of L-valine, L-leucine, and DL-isoleucine was suppressed in drought-tolerant TaPYLox under drought stress, suggesting that drought-tolerant wheat might be low in these amino acids. 3-dehydroshikimic acid and α-ketoglutaric acid were decreased by drought stress in an ABA-independent manner. In this study, we have succeeded in identifying metabolites that are regulated by drought stress in an ABA-dependent and -independent manner. The findings of this study should be useful for future breeding of drought-tolerant wheat.