HAIRY‐SHEATH FRAYED #1‐O: A SYSTEMIC, HETEROCHRONIC MUTANT OF MAIZE THAT SPECIFIES SLOW DEVELOPMENTAL STAGE TRANSITIONS

Abstract

Hairy sheath frayed‐1 (Hsf1‐O), an ethyl methanesolfonate‐induced dominant mutant in maize, was first described as an excessively hairy plant with pronglike projections of sheath that extended from the margin of the leaf blade. We describe several other phenotypes and show that Hsf1‐O affects virtually every segment of the plant. We have identified genetic backgrounds that suppress some of the Hsf1‐O phenotypes. The morphological descriptions reveal a prolongation of cell differentiation in certain tissues and organs. In general, transformations are from more adult to more juvenile, not older to younger. On the assumption that Hsf1‐O acts with the same developmental logic in both the apical meristem and leaf primordia, the leaf sheath is a juvenile blade, not a young blade. Genetic background effects show that the expressivity of the phenotype is influenced by the plant's time to anthesis. The suppression and temporal shift in Hsf1‐O expression patterns in early flowering lines is due to the inherent accelerated maturation of cells in these lines. In early flowering lines, transformations are suppressed and shifted toward the less mature (younger) tissues, organs, and segments of the plant. We conclude that Hsf1‐O is a heterochronic mutation that prolongs the time to maturity (delays terminal differentiation), and that a primordial cell's developmental maturity rather than the cell's position can dictate that cell's fate. Hsf1‐O disconnects the rate of developmental stage transition from the overall flowering‐time rate.