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Alvarez-Gerding, X., Cortes-Bullemore, R., Medina, C., Romero-Romero, J. L., Inostroza-Blancheteau, C., Aquea, F., et al. (2015). Improved Salinity Tolerance in Carrizo Citrange Rootstock through Overexpression of Glyoxalase System Genes. Biomed Res. Int., 827951, 7 pp.
Abstract: Citrus plants are widely cultivated around the world and, however, are one of the most salt stress sensitive crops. To improve salinity tolerance, transgenic Carrizo citrange rootstocks that overexpress glyoxalase I and glyoxalase II genes were obtained and their salt stress tolerance was evaluated. Molecular analysis showed high expression for both glyoxalase genes (BjGlyI and PgGlyII) in 5H03 and 5H04 lines. Under control conditions, transgenic and wild type plants presented normal morphology. In salinity treatments, the transgenic plants showed less yellowing, marginal burn in lower leaves and showed less than 40% of leaf damage compared with wild type plants. The transgenic plants showed a significant increase in the dry weight of shoot but there are no differences in the root and complete plant dry weight. In addition, a higher accumulation of chlorine is observed in the roots in transgenic line 5H03 but in shoot it was lower. Also, the wild type plant accumulated around 20% more chlorine in the shoot compared to roots. These results suggest that heterologous expression of glyoxalase system genes could enhance salt stress tolerance in Carrizo citrange rootstock and could be a good biotechnological approach to improve the abiotic stress tolerance in woody plant species.
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Romero-Romero, J. L., Inostroza-Blancheteau, C., Orellana, D., Aquea, F., Reyes-Diaz, M., Gil, P. M., et al. (2018). Stomata regulation by tissue-specific expression of the Citrus sinensis MYB61 transcription factor improves water-use efficiency in Arabidopsis. Plant Physiol. Biochem., 130, 54–60.
Abstract: Water-use efficiency (WUE) is a quantitative measurement of biomass produced per volume of water transpired by a plant. WUE is an important physiological trait for drought response to mitigate the water deficiency. In this work, a cisgenic construction from Citrus sinensis was developed and its function in the improvement of WUE was evaluated in Arabidopsis. Sequences of the CsMYB61 coding region, a transcription factor implicated in the closure of stomata, together with a putative stomata-specific promoter from CsMYB.1.5, were identified and cloned. The protein encoded in the CsMYB61 locus harbors domains and motifs characteristic of MYB61 proteins. In addition, a 1.2 kb promoter region of the gene CsMYB15 (pCsMYB15) containing regulatory elements for expression in guard cells and in response to Abscisic Acid (ABA) and light was isolated. In Arabidopsis, pCsMYB15 directs the expression of the reporter gene GUS in stomata in the presence of light. In addition, transgenic lines expressing the CsMYB61 coding region under transcriptional control of pCsMYB15 have a normal phenotype under in vitro and greenhouse conditions. These transgenic lines exhibited a smaller opening of the stomata pore, lower stomatal conductance and respiration rate, enhanced sensitivity to exogenous ABA, and high drought stress tolerance. Our results indicate that stomata-specific expression of CsMYB61 enhances water use efficiency under drought conditions in Arabidospis.
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Romero-Romero, J. L., Inostroza-Blancheteau, C., Reyes-D?az, M., Matte, J. P., Aquea, F., Espinoza, C., et al. (2020). Increased Drought and Salinity Tolerance in Citrus aurantifolia (Mexican Lemon) Plants Overexpressing Arabidopsis CBF3 Gene. J. Soil Sci. Plant Nutr., 20(1), 244–252.
Abstract: Citrus are a globally important fruit crop. Abiotic stressors such as drought and salinity adversely affect physiological citrus performance and survival. With the aim of improving drought tolerance in citrus plants, we constructed transgenic lines of Citrus lemon overexpressing the Arabidopsis transcription factor CBF3. Molecular, physiological, and quantitative real-time analyses showed high expression of AtCBF3 in three selected transgenic lines. During a 15-day treatment of water deficit by cessation of irrigation, the transgenic lines LM2 and LM14 showed lower stomatal conductance and transpiration paired with lower photosynthesis, whereas transgenic line LM7 maintained its photosynthesis, declining stomatal conductance, and transpiration compared to WT plants, which is manifested into more efficient water use. The genes CsRafS1 and CsGolS1 showed similar or greater expression in one of the transgenic lines with respect to control plants. Moreover, transgenic lines were more tolerant to saline stress and presented a greener phenotype with increased chlorophyll content in leaf discs compared to WT plants. In addition, a lower electrical conductivity in solution was observed in transgenic lines. Furthermore, all transgenic lines exhibited significantly less accumulation of reactive oxygen species than WT plants. Together, these results suggest the potential for heterologous expression of the AtCBF3 gene to mediate tolerance to hydric and saline stress in citrus plants.
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