Mis-regulation of SlUVI4 and SlCCS52B leads to repressed hypocotyl elongation.
To further determine the role of SlUVI4 and SlCCS52Bplayed in hypocotyl elongation, we generated sluvi4 mutants using Crispr-Cas9 technology and SlCCS52B overexpression lines in Arabidopsis. We obtained several mutants with different mutation types. Tomato plants with mutations in the second exon of SlUVI4 at T1 generation could not set up fruits, and we conducted reciprocal crosses with wild type plants ‘Heinz 1706’ and did not get success suggesting that the second exon is pivotal for SlUVI4 function. Interestingly, all of mutants with the capability of fruiting only had mutations in the first exon, and the number of missing nucleotides is a multiple of 3, resulting in truncated proteins of SlUVI4 (Figure S9). Mutants of sluvi4 cr-1 and sluvi4 cr-2 lost 6 and 42 nucleotides encoding 2 and 14 amino acids, respectively. Both mutants exhibited significantly shorter hypocotyls than wild type, andsluvi4 cr-1 phenotype was weaker than that of sluvi4 cr-2(Figure 10 A, B). Both mutants had thicker hypocotyls than wild type (Figure 10C). Cell cycle analysis revealed that sluvi4 mutants had enhanced endoreduplication indicated by more 8C and 16C and a higher EI (Figure 10D). We further investigated three independent overexpression lines of SlCCS52B in Arabidopsis, which had significantly shorter hypocotyls compared to wild type (Figure 11). Cell cycle analysis revealed that overexpression of SlCCS52B also promoted endoreduplication in hypocotyl cells compared to wild type. Meanwhile, we obtained overexpression lines of SlCCS52A2 in tomato, and three independent lines exhibited shorter hypocotyls without the alteration of cell cycle progression (Figure S10). All these data indicated that mis-regulation of SlUVI4 and SlCCS52Baffects tomato hypocotyl elongation through the modulation of cell cycle progression.