CYP78A5 encodes a cytochrome P450 that marks the shoot apical meristem boundary in Arabidopsis

The normal development of shoot structures depends on controlling the growt h, proliferation and differentiation of cells derived from the shoot apical meristem. We have identified the CYP78A5 gene encoding a putative cytochro me P450 monooxygenase that is the first member of the CYP78 family from Ara bidopsis. This gene is strongly expressed in the peripheral regions of the vegetative and reproductive shoot apical meristems, defining a boundary bet ween the central meristematic zone and the developing organ primordia. In a ddition, CYP78A5 shows a dynamic pattern of expression during floral develo pment. Overexpression of CYP78A5 affects multiple cell types, causing twist ing and kinking of the stem and defects in floral development. To define th e relationship of CYP78A5 to genes controlling meristem function, we examin ed CYP78A5 expression in plants mutant for SHOOT MERISTEMLESS, ZWILLE and A RGONAUTE, and have found that CYP78A5 expression is altered in these mutant backgrounds. We propose that CYP78A5 has a role in regulating directional growth in the peripheral region of the shoot apical meristem in response to cues established by genes regulating meristem function.