A zinc-finger transcription factor LGA1 negatively regulates lateral growth in Arabidopsis and trees

Lateral growth in plants originates from the vascular cambium, where stem cells are located. Cambium provides thickness to plant organs by generating the conductive tissues - xylem (wood) toward the centre and phloem toward the organ periphery. Vascular development continues as long as the plant grows, and proliferation and differentiation of these tissues from the cambium is under strict control. Besides its fascinating theoretical significance, understanding cambial regulation has also a significant applied value because this knowledge brings us powerful tools to manipulate growth and enhance biomass production in trees in an ever-changing environment. Through a functional genomics approach, we have recently identified that a novel zinc-finger transcription factor LATERAL GROWTH-ASSOCIATED 1 (LGA1) is expressed preferentially in the vascular tissues and activated by the plant hormone cytokinin, an enhancer of cambial cell division rate and lateral growth in plants. Unexpectedly, instead of priming radial growth, overexpression of LGA1 in Arabidopsis thaliana roots or hybrid aspen stems suppresses cell divisions and resulting xylem production. In comparison, loss-of-function lga1 plants often had increased number of cells in root vasculature and results in increased lateral growth. To study the molecular mechanisms behind LGA1 action, we performed RNA-seq analysis in the mutant roots that are going through secondary growth. Our results showed that LGA1 induction activates the expression of genes associated with stress signalling pathways, while repressing the expression of genes associated with cytokinin responses. Altogether, these results culminate to the fact that LGA1 is a negative regulator of secondary growth and represses cell division activity in plants, while balancing the plant responses to various stress factors.