Practice question

SHOOT MERISTEMLESS encodes KNOX1 class homeobox protein expressed throughout shoot apical meristem dome but sharply downregulated in incipient leaf primordia by ASYMMETRIC LEAVES1/2 repression pathway. STM prevents premature differentiation by promoting cytokinin biosynthesis through IPT7 activation, repressing gibberellin 20-oxidase genes maintaining low active GA, repressing CUC boundary regulators at proper domains, and protecting stem cell identity. Strong stm mutants fail to establish embryonic SAM, exhibit fused cotyledons, lack vegetative growth, arrest as seedlings, demonstrating absolute requirement for maintaining shoot meristem identity and indeterminate self-renewal capacity.