Application of HB17, an Arabidopsis class II homeodomain-leucine zipper transcription factor, to regulate chloroplast number and photosynthetic capacity

Abstract

Transcription factors are proposed as suitable targets for the control of traits such as yield or food quality in plants. This study reports the results of a functional genomics research effort that identified ATHB17, a transcription factor from the homeodomain-leucine zipper class II family, as a novel target for the enhancement of photosynthetic capacity. It was shown that ATHB17 is expressed natively in the root quiescent centre (QC) from Arabidopsis embryos and seedlings. Analysis of the functional composition of genes differentially expressed in the QC from a knockout mutant (athb17-1) compared with its wild-type sibling revealed the over-representation of genes involved in auxin stimulus, embryo development, axis polarity specification, and plastid-related processes. While no other phenotypes were observed in athb17-1 plants, overexpression of ATHB17 produced a number of phenotypes in Arabidopsis including enhanced chlorophyll content. Image analysis of isolated mesophyll cells of 35S::ATHB17 lines revealed an increase in the number of chloroplasts per unit cell size, which is probably due to an increase in the number of proplastids per meristematic cell. Leaf physiological measurements provided evidence of improved photosynthetic capacity in 35S::ATHB17 lines on a per unit leaf area basis. Estimates of the capacity for ribulose-1,5-bisphosphate-saturated and -limited photosynthesis were significantly higher in 35S::ATHB17 lines.

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

“…Under normal conditions, we found that ATHB17 was primarily expressed in the root, with weak expression in the shoot, consistent with the previous report36. However, Hymus et al 34. only detected very weak ATHB17 signal in specific cells in the embryonic, QC area of primary and lateral roots, through in situ hybridization analysis.…”

“…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 ., ).…”

“…Case no. 3: effects of variation in grain yield on evaluation of maize hybrids with biotechnology-derived transcription factor technology Monsanto has developed a biotechnology-derived inbred line of maize that expresses HB17 (ATHB17), a transcription factor from A. thaliana (Hymus et al, 2013;Park et al, 2013). Expression of ATHB17 in hybrid maize is associated with increased ear biomass at silking compared to near-isogenic controls (Rice et al, 2014).…”

Cellular perspectives for improving mesophyll conductance

“…A number of mutants in chloroplast division machinery have been identified, although they generally lead to fewer, larger plastids, which is likely to decrease the ability of a cell to optimize the spatial distribution of its photosynthetic machinery for CO 2 uptake (Chen et al , ). Although the promotion of chloroplast differentiation can be engineered (Wang et al , ), quantitatively manipulating chloroplast number and size in mesophyll cells remains a major challenge (Hymus et al , ). A simpler route to increasing the number of chloroplasts per cell (and thus S c ) may be to decrease mesophyll cell size (see previous section).…”