Fruit set and development are affected by many phytohormones, including gibberellin.  Little is known regarding molecular mechanism underlying gibberellin mediated fruit set and development especially in Capsicum.  Three gibberellin receptors, CaGID1b.1, CaGID1b.2 and CaGID1c, and a DELLA protein, CaGAI, have been identified in Capsicum annuum L.  During the fruit development, the expression level of CaGID1c was low, and the expression fold change is mild.  However, CaGID1b.1 and CaGID1b.2 were relatively higher and more acute, which indicates that CaGID1b.1 and CaGID1b.2 may play an important role in fruit pericarp, placenta and seed.  Ectopic expressions of CaGID1b.1, CaGID1b.2 and CaGID1c in Arabidopsis double mutant gid1a gid1c increased plant height, among which CaGID1b.2 had the most significant effect; CaGAI reduced plant height in double mutant rga-24/gai-t6, having a similar function to AtGID1 and AtGAI in stem elongation.  Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays indicated that CaGID1b.1 and CaGID1b.2 interact with CaGAI in a GA-dependent manner, while CaGID1c interacts with CaGAI in a GA-independent manner.  Our study reveals the key elements during gibberellin signaling in Capsicum and supports the critical importance of gibberellin for Capsicum fruit set and development.

Low temperature and high salinity are the major abiotic stresses that restrict cucumber growth and production, breeding materials with multiple abiotic resistance are in greatly need. Here we investigated the effect of introducing the LOS5 gene, a key regulator of ABA biosynthesis in Arabidopsis thaliana, under the stress-responsive RD29A promoter into cucumber (Cucumis sativus L. cv. S516). We found that T1 RD29A-LOS5 transgenic lines have enhanced tolerance to cold and salt stresses. Specifically, transgenic lines exhibited dwarf phenotypes with reduced leaf number, shorter internode, decreased length of the biggest leaf, fewer female flowers, shorter fruit neck and lower vitamin C (Vc). The increased cold tolerance can be reflected from the significantly decreased cold index, the reduced electrolyte leakage index and the MDA content upon cold treatment as compared to those in the control. This may result from the accumulation of internal ABA, soluble sugars and proline, and the enhanced activities of protective enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the transgenic lines. Under salt treatment, the transgenic lines exhibited increased germination index, vigor index, more lateral roots and increased root fresh weight. Moreover, RD29A-LOS5 transgenic plants displayed quicker responses in salt stress than that in low-temperature stress.

Low light stress is one of the main limiting factors which influence the production of sweet pepper under protected cultivation in China. In this experiment, two genotypes of sweet pepper, ShY (low light-tolerant genotype) and 20078 (low light-sensitive genotype), were used to study the effects of low light (photosynthetic photon flux density, PPFD was 75- 100 μmol m-2 s-1, control 450-500 μmol m-2 s-1) on photosynthesis during leaf development. The result indicated that under low light chlorophyll content, net photosynthetic rate (PN), photosynthetic apparent quantum efficiency ( i) and carboxylation efficiency (CE) of sweet pepper leaves increased gradually and decreased after reaching the maximum levels. The time to reach the peak values for all the above parameters was delayed, whereas the light compensation point (LCP) decreased gradually along with leaf expansion. The decrease in maximum quantum yield of PS II (Fv/Fm) was not observed at any stages of the leaf development under low light condition, but the actual PS II efficiency under irradiance ( PS II) was lower accompanied by an increased non-photochemical quenching (NPQ) in young and/or old leaves compared with mature leaves. The antenna thermal dissipation (D) was a main way of heat dissipation when young leaves received excessive light energy, while the decline in photosynthetic function in senescence leaf was mostly owing to the decrease in carbon assimilation capacity, followed by a significantly increased allocation of excessive energy (Ex). Compared with 20078, ShY could maintain higher PN, PS II and lower QA reduction state for a longer time during leaf development. Thus, in ShY photosynthetic efficiency and the activity of electron transport of PS II were not significantly affected due to low light stress.