Prompt: The research team lead by Pro Cheng Yunjiang from the College of Horticulture & Forestry Sciences published their latest findings entitled “CsMYB96 confers water loss resistance in citrus fruit by simultaneous regulation of water transport and wax biosynthesis” in Journal of Experimental Botany. Based on the study of aquaporins AQPs, the team analyzed the regulatory mechanism of water movement in postharvest citrus fruits in detail.
As an important intracellular solvent, water functions significantly in processes of plant growth and its post-harvest. A comprehensive analysis of transcriptomic and metabolomic profiling has revealed that postharvest water loss may be a key factor that leads to quality deterioration and senescence in citrus fruits.
The research team found that most plasma membrane intrinsic proteins (CsPIPs), were consistently down-regulated in the process of postharvest water loss of citrus fruit, among which CsPIP2;4 was further characterized as the predominant GsPIP with high expression in the peel of postharvest citrus fruit and high-water channel activity. After 5 hours, the water loss in kumquat fruits with transient expression of CsPIP2;4 was evidently higher than that in the control group, which indicated that the lower expression of CsPIP2;4 would alleviate postharvest water loss.
Negative regulation on postharvest water loss in citrus fruit by CsPIP2;4
The in silico analysis further revealed that the expression of CsMYB96 had a significant negative correlation with that of CsPIPs. In vitro and in vivo experiments confirmed that CsMYB96 can directly repress the expression of CsPIPs. To further confirm the function of CsMYB96 to reduce water loss in citrus fruit, the team conducted function assays of CsMYB96 by transient overexpression in Kumquat fruit and stable overexpression in Arabidopsis. This study found that overexpression of CsMYB96 could lead to down-regulation of homologs PIP2;4 in Arabidopsis thaliana and Kumquat fruit, which would significantly reduce water loss of citrus fruits and Arabidopsis.
Regulation of water movement in fruit and Arabidopsis by CsMYB96
Previous studies have shown that MYB96 in Arabidopsis can positively regulate several genes in the wax synthesis metabolic pathway, thus directly affecting the leaves wax synthesis process. Therefore, in this study, the team examined the wax composition of the kumquat fruit with transient overexpression of CsMYB96 and of Arabidopsis thaliana with stable transformation, finding that overexpression of CsMYB96 significantly increased the total amount of wax in the peel of kumquat and Arabidopsis thaliana. Further in vivo and in vitro experiments showed that CsMYB96 could directly bind to cis-elements in the promoters of wax-related genes and activate their expression.
In the present study, besides its role in wax biosynthesis by inducing wax-related genes, citrus MYB96 was also found to be involved in water transport by suppressing AQPs, which can help to reduce the water loss of citrus fruit. Our results provide some new insights into the regulatory mechanism of water movement and cuticle barrier(wax) formation in citrus fruit. The findings may facilitate a better understanding of plant strategies in response to water loss.
Zhang Mingfei, a doctoral student graduating from HZAU, is the first author of the thesis. Professor Cheng Yunjiang and Dr. Zhu Feng are the co-corresponding authors. Participating researchers included Wang Jinqiu (associate professor of Chengdu University), Liu Ruilian (a graduate student of HZAU), Liu Hai, Yang Hongbin and Zhu Zhifeng (doctoral students of HZAU). This research was supported by National Key R&D Program of China, National Natural Science Foundation of China and National modern agricultural industrial technology system.
Source:https://academic.oup.com/jxb/advance-article/doi/10.1093/jxb/erab420/6380295?login=true
Translated by: Liu Binbin
Supervised by: Wang Xiaoyan
