Cucumber Hypocotyl Elongation Mutants Reveal New Players in Plant UVB Signaling

In Arabidopsis, the UVR8-mediated signaling pathway is employed to attain UVB protection and acclimation to deal with low dosage UVB (LDUVB)-induced stresses. we identified SHORT HYPOCOTYL1 (SH1) in cucumber which regulates LDUVB-dependent hypocotyl elongation by modulating the UVR8 signaling pathway. We show that hypocotyl elongation in cucumbers carrying the recessive sh1 allele was LDUVB-insensitive and Sh1 encoded a human SMARCA3-like chromatin remodeling factor. The allele frequency and distribution pattern at this locus among natural populations supported the wild cucumber origin of sh1 for local adaptation, which was under selection during domestication. The SH1 protein sequence was highly conserved among eukaryotic organisms, but its regulation of hypocotyl elongation in cucumber seems to be a novel function. Sh1 transcript abundance was highly correlated with hypocotyl elongation rate and the expression level of cell elongation-related genes. Expression profiling of key regulators in the UVR8 signaling pathway revealed significant differential expression of CsHY5 between two near isogenic lines of Sh1. Sh1 and CsHY5 acted antagonistically at transcriptional level. We are also characterizing two LDUVB-insensitive, long hypocotyl mutants (lh1 and lh2). Their possible roles in LDUVB-dependent hypocotyl elongation in the UVR8-mediated signaling pathway will be discussed.