Molecular genetic regulation of de novo assembly of shoot meristem in Arabidopsis

Abstract

Abstract: Totipotency is a hallmark of plants, where entire shoots/roots can be formed de novo from undifferentiated callus in response to external inductive cues. Interestingly, during de novo shoot organogenesis, only a few initial cells known as ‘progenitor’ can develop into an entire shoot system. How these initials are selected and what governs their subsequent progression to a patterned organ system remain unresolved. My work led to the discovery of a new regulatory axis where shoot-promoting factor CUC2 activates the expression of cell wall loosening enzyme XTH9 in the cells surrounding the progenitors. Encapsulation of progenitors by a shell of cells expressing cell wall loosening enzyme serves as a mechanism for selecting productive progenitors in undifferentiated callus. CUC2-XTH9 activates cell polarity non-cell autonomously to confer the productive fate to regenerating progenitors. Interestingly, cell wall modification in surrounding non-progenitor cells and cell polarity in the progenitors act in a regulatory feedback loop to make the dome-shaped shoot meristem de novo. Together, my studies provide a simple model accountable for self-organized morphogenesis in the absence of pre-pattern cues. CUC2 expression is activated by plant-specific transcription factor PLETHORA. PLETHORA proteins control a variety of developmental and regenerative processes in Arabidopsis. I have examined the role of monocot, Rice PLETHORA genes in dicot plants, Arabidopsis. My studies reveal the conserved function of Rice PLETHORA proteins in controlling both developmental processes, such as lateral root outgrowth, and regenerative responses, such as regeneration of damaged tissues or complete shoot system in evolutionary diverged dicot plant species.