Expression of a Truncated ATHB17 Protein in Maize Increases Ear Weight at Silking

Abstract

ATHB17 (AT2G01430) is an Arabidopsis gene encoding a member of the α-subclass of the homeodomain leucine zipper class II (HD-Zip II) family of transcription factors. The ATHB17 monomer contains four domains common to all class II HD-Zip proteins: a putative repression domain adjacent to a homeodomain, leucine zipper, and carboxy terminal domain. However, it also possesses a unique N-terminus not present in other members of the family. In this study we demonstrate that the unique 73 amino acid N-terminus is involved in regulation of cellular localization of ATHB17. The ATHB17 protein is shown to function as a transcriptional repressor and an EAR-like motif is identified within the putative repression domain of ATHB17. Transformation of maize with an ATHB17 expression construct leads to the expression of ATHB17Δ113, a truncated protein lacking the first 113 amino acids which encodes a significant portion of the repression domain. Because ATHB17Δ113 lacks the repression domain, the protein cannot directly affect the transcription of its target genes. ATHB17Δ113 can homodimerize, form heterodimers with maize endogenous HD-Zip II proteins, and bind to target DNA sequences; thus, ATHB17Δ113 may interfere with HD-Zip II mediated transcriptional activity via a dominant negative mechanism. We provide evidence that maize HD-Zip II proteins function as transcriptional repressors and that ATHB17Δ113 relieves this HD-Zip II mediated transcriptional repression activity. Expression of ATHB17Δ113 in maize leads to increased ear size at silking and, therefore, may enhance sink potential. We hypothesize that this phenotype could be a result of modulation of endogenous HD-Zip II pathways in maize.

ATHB17 enhances stress tolerance by coordinating photosynthesis associated nuclear gene and ATSIG5 expression in response to abiotic stress

“…RNA-seq profiling analysis revealed that ATHB17 acted as a repressor of PhANGs. ATHB17 was reported as a transcriptional repressor containing EAR (ERF-associated amphiphilic repression)-like motif35. Consistent with this result, we found that ATHB17 repressed the transcription of 26 PhANGs under normal or salt stress conditions (Table 2 and Fig.…”

“…We found full length ATHB17 protein had strong self-activation activity. It has been reported that ATHB17 protein lacking the first 113 amino acids (ATHB17Δ113) can still homo-dimerize and specifically recognize the sequence requirements for DNA binding35. Thus we used ATHB17 protein lacking the first 107 amino acids (ATHB17Δ107) for Y1H and electrophoretic mobility shift assay (EMSA).…”

“…Overexpression of ATHB17 in Arabidopsis enhances chlorophyll content in the leaves, while expression of a truncated ATHB17 protein in maize increases ear weight at silking3435. ATHB17 -overexpressing Arabidopsis plants are sensitive to ABA and NaCl, whereas ATHB17 knockout mutants are insensitive to ABA and NaCl at post germination stage.…”

Comparative analysis of maize (Zea mays) crop performance: natural variation, incremental improvements and economic impacts

“…Monsanto has developed a biotechnology‐derived inbred line of maize that expresses HB17 (ATHB17), a transcription factor from A. thaliana (Hymus et al ., ; Park et al ., ). Expression of ATHB17 in hybrid maize is associated with increased ear biomass at silking compared to near‐isogenic controls (Rice et al ., ). Increased ear biomass at an early stage of plant development may be indicative of increased sink size and an overall greater grain yield opportunity from hybrid maize at harvest (Borras and Westgate, ; Borras et al ., ; Jones et al ., ; Lee and Tollenaar, ).…”

Evaluating maize phenotypic variance, heritability, and yield relationships at multiple biological scales across agronomically relevant environments

“…There have been copious reports of breakthroughs related to yield improvement and stress tolerance through biotechnology approaches, both in model species (Karaba et al, ; Kirst, Gabilly, Niyogi, Lemaux, & Melis, ; Kromdijk et al, ; Miwa, Takano, & Fujiwara, ; Sade et al, ; Van Camp, ), and in crops (Castiglioni et al, ; Nelson et al, ; Nuccio et al, ; Preuss et al, ; Rice et al, , Nemali et al, ). In many cases, there are reports of yield improvement with limited number of tested environments, and in no known cases, are there reports across multiple germplasm.…”