Tomato hypocotyl elongation is a consequence of active cell division and expansion, both of which require precisely regulated cell cycle progression. Little is known about the function of APC/C regulators in cell cycle progression during hypocotyl growth. Here, we isolated and characterized the positive and negative APC/C regulators, SlCCS52 and SlUVI4 genes in tomato. We probed SlUVI4 and SlCCS52B roles in tomato hypocotyl elongation via modulating cell cycle progression. Light especially blue light represses the transcription of SlUVI4 and SlCCS52B to inhibit the hypocotyl elongation through the suppression of endoreduplication. MS basal salts and sugar both improve SlUVI4 and SlCCS52B transcription to enhance hypocotyl length via the promotion of endoreduplication. Hypocotyl elongation enhanced by heat might require auxin-induced repression of SlUVI4 transcription. Salt inhibits hypocotyl elongation possibly through ethylene-mediated modulation of SlUVI4 and SlCCS52B transcription. Genetic studies reveal that tomato deletion mutant of SlUVI4 and overexpression plants of SlCCS52B in Arabidopsis both exhibit shorter hypocotyl with enhanced endoreduplication. Thus, our results suggest that APC/C activities stimulated by SlCCS52 genes requires SlUVI4-meidated inhibitory machinery to reorchestrate cell cycle progression and facilitate hypocotyl elongation.

Iron (Fe) is an essential element for plant growth, development, and metabolism. Due to its lack of solubility and low bioavailability in soil, Fe levels are usually far below the optimum amount for most plants’ growth and development. In apple production, excessive use of nitrogen fertilizer may cause iron chlorosis symptoms in the newly growing leaves, but the regulatory mechanism is unclear. In this study, it was found that low nitrate (NO3-, LN) application could alleviate the symptoms of Fe deficiency, LN treatment promoted lower the rhizosphere pH, which was beneficial for root Fe acquisition, meanwhile, LN treatment increased citrate and abscisic acid (ABA) accumulation in root, which promoted Fe transport from root to shoot and maintained Fe homeostasis. Moreover, RNA-Seq and qRT-PCR analysis showed that nitrate application caused differential expression of genes that were related to Fe uptake and transport as well as transcriptional regulators. In summary, our data reveal that low nitrate alleviated Fe deficiency through multiple pathway, which exhibits a new option for attenuating Fe deprivation by regulating the balance between nutrients.