RSS1 is a negative regulator of hypocotyl elongation growth. Phenotype analysis of 7-d-old WT (Col-0), homozygous T-DNA insertion mutant rss1 and transgenic overexpression lines (OE1, OE2, OE3) along with vector control (VC) seedlings growing under (a) long day conditions and (b) continuous darkness. The hypocotyls of rss1 mutants were significantly longer than WT while RSS1OE2 seedlings had relatively shorter hypocotyls. (c) Micrograph of hypocotyls of WT, rss1 and RSS1OE2 seedlings (Bars = 20 μm). (d) Quantification of hypocotyl epidermal cell length of WT, rss1 and RSS1OE2seedlings. Values represent the average from two biological replicates each having 15 seedlings and error bars represent SE. (Student’s t-test; P < 0.01; **WT vs. mutant).