A paper recently published by Ployet et al. (2019) in New Phytologist provides insights into regulatory mechanisms of wood formation under stressful conditions, particularly elucidating regulator co‐opting by K‐fertilization and/or water limitation that may potentially promote adaptive wood traits.
Their integrated network‐based approach enabled them to identify meaningful biological processes and regulators impacted by K‐fertilization and/or water limitation. It revealed that modules of co‐regulated genes and metabolites strongly correlated to wood complex traits are in the heart of a complex trade‐off between biomass production and stress responses. Nested in these modules, potential new cell‐wall regulators were identified, as further confirmed by the functional characterization of EgMYB137.
EgMYB137 is involved in xylem formation in Eucalyptus roots. GUS expression driven by the EgMYB137 promoter was observed in the main root of Eucalyptus grandis transgenic lines, in (a) vascular tissues (in vitro, young root tip), (b) xylem vessels (differentiation zone) and (c) axial parenchyma cells surrounding the youngest vessels immediately below the cambium (5‐month‐old roots). Observations were made in brightfield mode on free‐hand cut sections. White arrowheads represent vessels. Co, cortex, Cz, cambial zone, Ph, phloem; Xy, xylem. (d) Five‐month‐old Eucalyptus roots observed under epifluorescence microscopy. Highest autofluorescence intensity is observed in the cell wall (CW) of vessels and axial parenchyma cells immediately below the cambium (white arrowhead). (e) Brightfield observations of semithin section of 5‐month‐old control root (empty vector) stained with toluidine blue. Cz, cambial zone; Xy, xylem. (f) Brightfield observations of semithin section of 5‐month‐old p35S:EgMYB137 roots, showing an increase in fiber CW thickness. (g) Changes in CW thickness of vessels and fibers in p35S:EgMYB137 root xylem. Vessel SCWs were significantly thinner in p35S:EgMYB137 lines (1.99 ± 0.04 μm) as compared to control lines (2.07 ± 0.06 μm). Fiber SCWs were significantly thicker in p35S:EgMYB137 lines (2.60 ± 0.05 μm) as compared to control lines (2.29 ± 0.04 μm). ***, P < 0.0001 (Student’s t‐test). (h) Decrease in vessel density in p35S:EgMYB137 root xylem (10.4 ± 1.4 mm−2) as compared to control (16.1 ± 3.1 mm−2). *, P < 0.05 (Student’s t‐test). Error bars represent SD (n = 6 for transgenic lines, n = 4 for controls). Vessel CW thickness was measured on > 70 vessels and > 1200 fibers. Vessel density and lumen diameter were measured on > 440 vessels and > 1200 fibers. Scale bars, (a) 200 μm; (b) 500 μm; (c–d) 150 μm; (e–f) 50 μm.
