| During the plant lifecycle, lateral organs will take on various shapes and functions depending on the changing needs of the plant. While much is known about the pathways that control the identity of these organs, little has been uncovered as to how the shape or the distribution of cell types is determined. Here I present the characterization of a duplicate pair of C 2H2 zinc-finger type transcription factors, JAGGED and NUBBIN, which are important regulators of organ shape. JAG is expressed during organ initiation, and in regions of organs undergoing active growth where it is required to prevent the premature differentiation of tissues during organogenesis. Gain-of-function studies show that JAG is sufficient to promote tissue growth and can rescue the development of the cryptic bract, a vestigial organ in Arabidopsis that develops in other flowering plants. NUB expression partially overlaps with that of JAG but is expressed more exclusively and in a polar fashion in lateral organs. While nub single mutants have no abnormal phenotype, jag nub double mutants develop strong patterning defects in stamens where JAG/NUB activity promotes the development of the pollen-bearing locules. In the gynoecium, an analysis of cell size and number revealed that JAG and NUB are necessary to promote valve growth and cellular differentiation. Further characterization of JAG revealed other roles in controlling tissue identity in the fruit. In Arabidopsis, fruits develop a specialized tissue termed the valve margin that enables the fruit to shatter apart at maturity to disperse the seeds. JAG acts with two YABBY-family transcription factor genes, FILAMENTOUS FLOWER (FIL) and YABBY3 (YAB3) to promote the formation of the valve margin by maintaining the expression of the SHATTERPROOF (SHP) genes. JAG, FIL and YAB3 further regulate the development of the valve margin by activating the expression of FRUITFULL, which prevents SHP activity from expanding into the seed-pod walls, or valves. Valve margin development is further restricted by REPLUMLESS (RPL), which limits the activity of JAG and FIL, preventing these genes from activating SHP in the replum. Together, these studies identify JAG and NUB as important regulators of organ shape and tissue pattering. |
