Plants are immobile organisms, which growth driven by turgor pressure is plastic in concert with surrounding environments. As plant cells work as a fundamental unit in plant growth, morphogenesis and development of any tissue can be interpreted as the actions of plant cells programmed in differentiation, proliferation, growth, and maturation. Plant cell wall that represents a characteristic cell structure is related to most of above cellular processes, especially playing a determinant role in cell morphogenesis.
Cell growth includes two fundamental events: cell expansion and wall reinforcement. Cell expansion requires cell wall relaxed. While expansion, newly synthesized polysaccharides are integrated into the walls to confer plant cells with distinct shape, size and function. Plants hence have evolved complex mechanisms to coordinate the two cellular events during cell growth. However, the combinatorial mechanism that integrates different regulatory pathways to orchestrate cell expansion and wall strengthening remains elusive.
The group of Prof. ZHOU Yihua from the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, recently reported that rice homeobox protein KNAT7 interacts with a growth master regulator, GRF4, and a secondary wall regulator, NAC31, to coordinate cell expansion and wall thickening in fiber cells.
They identified a rice class II KNOX-like homeobox member KNAT7 that integrates the regulatory pathways of cell expansion and wall strengthening via forming distinct protein complexes. Mutation in KNAT7 resulted in enhanced secondary wall biosynthesis and cell expansion in the mutant internodes and grain glumes; overexpression of KNAT7 gave rise to the opposite effects. KNAT7 interacted with the secondary wall key regulator NAC31 and the master cell growth factor GRF4 to repress their downstream regulatory pathways.
Moreover, performing anatomical analysis and examining the expression of KNAT7 and its interacting partners NAC31 and GRF4 in the developing internodes and panicles corroborated the spatiotemporal actions of the KNAT7-GRF4 and KNAT7-NAC31 modules.
This finding in identifying KNAT7 as an integrative regulator to control cell morphogenesis, offers a mechanistic view for combinatorial modulation of plant cell growth and may provide a tool for the synergistic improvement of lodging resistance and grain yield in crops.
This work was published online in Plant Physiology entitled “Rice Homeobox Protein KNAT7 Integrates the Pathways Regulating Cell Expansion and Wall Stiffness” with Dr. WANG Shaogan and YANG Hanlei as the first authors on July 29, 2019 (DOI:10.1104/pp.19.00639). Prof. ZHOU Yihua and Dr. ZHANG Baocai are co-corresponding authors.
This research was supported by the Ministry of Agriculture of China, the National Natural Science Foundation of China, and Youth Innovation Promotion Association CAS, as well as the State Key Laboratory of Plant Genomics.
The working model of rice KNAT7 that integrates regulatory pathways of cell expansion and wall strengthening to coordinate fiber cell growth. (Image by IGDB)
Contact:
Mr. QI Lei
Institute of Genetics and Developmental Biology, Chinese Academy of Sciences
