Sasaki K, Ida Y, Kitajima S, Kawazu T, Hibino T, Hanba YT.

 Sci Rep. 2019 Oct 1;9(1):14121. doi: 10.1038/s41598-019-50610-5

 Abstract

 Alteration in the leaf mesophyll anatomy by genetic modification is potentially a promising tool for improving the physiological functions of trees by improving leaf photosynthesis. Homeodomain leucine zipper (HD-Zip) transcription factors are candidates for anatomical alterations of leaves through modification of cell multiplication, differentiation, and expansion. Full-length cDNA encoding a Eucalyptus camaldulensis HD-Zip class II transcription factor (EcHB1) was over-expressed in vivo in the hybrid Eucalyptus GUT5 generated from Eucalyptus grandis and Eucalyptus urophylla. Overexpression of EcHB1 induced significant modification in the mesophyll anatomy of Eucalyptus with enhancements in the number of cells and chloroplasts on a leaf-area basis. The leaf-area-based photosynthesis of Eucalyptus was improved in the EcHB1-overexpression lines, which was due to both enhanced CO₂ diffusion into chloroplasts and increased photosynthetic biochemical functions through increased number of chloroplasts per unit leaf area. Additionally, overexpression of EcHB1 suppressed defoliation and thus improved the growth of Eucalyptus trees under drought stress, which was a result of reduced water loss from trees due to the reduction in leaf area with no changes in stomatal morphology. These results gave us new insights into the role of the HD-Zip II gene.

See https://www.nature.com/articles/s41598-019-50610-5

Figure 1 (A) Gene expression levels measured using Northern blot analysis of the meristem, leaf, upper xylem, lower xylem, and root of the control GUT5 and EcHB1-overexpressed line EcHB1-2, in which actin2 of Eucalyptus camaldulensis (EcACT2) was used as the control (see Supplemental Information). (B) Phenotypes of the control (GUT5) and EcHB1-overexpressed lines (EcHB1-2 and EcHB1-10), grown for 12 months. (C) Tree growth traits such as stem diameter, tree height, growth rate in stem diameter and tree height, shoot fresh weight (FW), root FW and leaf number. Blank, gray, and filled bars indicate GUT5, EcHB1-2, and EcHB1-10, respectively. Means with standard errors are shown for 3–12 trees. Differences between lines were analyzed using one-way ANOVA, in which different letters indicate that the difference was statistically significant (P < 0.05).