Abstract
It is of critical importance for plants to correctly and efficiently allocate their resources between growth and defense to optimize fitness. Transcription factors (TFs) play crucial roles in the regulation of plant growth and defense response. Trihelix TFs display multifaceted functions in plant growth, development, and responses to various biotic and abiotic stresses. In our previous investigation of maize stalk rot disease resistance mechanism, we found a trihelix TF gene, ZmGT-3b, which is primed for its response to Fusarium graminearum challenge by implementing a rapid and significant reduction of its expression to suppress seedling growth and enhance disease resistance. The disease resistance to F. graminearum was consistently increased and drought tolerance was improved, while seedling growth was suppressed and photosynthesis activity was significantly reduced in the ZmGT-3b knockdown seedlings. Thus, the seedlings finally led to show a kind of growth–defense trade-off phenotype. Moreover, photosynthesis-related genes were specifically downregulated, especially ZmHY5, which encodes a conserved central regulator of seedling development and light responses; ZmGT-3b was confirmed to be a novel interacting partner of ZmHY5 in yeast and in planta. Constitutive defense responses were synchronically activated in the ZmGT-3b knockdown seedlings as many defense-related genes were significantly upregulated, and the contents of major cell wall components, such as lignin, were increased in the ZmGT-3b knockdown seedlings. These suggest that ZmGT-3b is involved in the coordination of the metabolism during growth–defense trade-off by optimizing the temporal and spatial expression of photosynthesis- and defense-related genes.
Highlights
The trihelix transcription factor (TF) family is one of the first families discovered in plants, and its family members are classified as GT factors because the GT element 5′-GGTTAA-3′ is the first cis-element isolated from these Transcription factors (TFs)
During the investigation of maize stalk rot disease resistance mechanism with nearisogenic lines (NILs), we found that the trihelix TF gene ZmGT-3b (GRMZM2G325038) was expressed at relatively high levels in non-inoculated R-NIL-seedling roots, but its expression was significantly decreased after inoculation (Supplementary Figure 1A)
The growth–defense trade-off in plants is associated with the limited availability of resources, which requires the plant to prioritize growth or defense, depending on dynamic external and internal factors
Summary
The trihelix transcription factor (TF) family is one of the first families discovered in plants, and its family members are classified as GT factors because the GT element 5′-GGTTAA-3′ is the first cis-element isolated from these TFs. The DNA-binding domain of these TFs features a typical trihelix structure (helix-loop-helix-loop-helix), that is, the helices form a bundle held together by a hydrophobic core that determines their specific binding to GT elements (Kaplan-Levy et al, 2012). Trihelix family members are grouped into five subfamilies, GT-1, GT-2, GT, SH4, and SIP, which were named after the first identified member of each subfamily. GT-1 proteins have one trihelix DNA-binding domain, GT-2 members have two DNA-binding domains, GT-1 and GT-2 members share high sequence similarity. Arabidopsis GT-1 directly activates the transcription of its target genes by stabilizing the TFIIA-TBPTATA components of the pre-initiation complex (Kaplan-Levy et al, 2012; Qin et al, 2014)
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