Research progress in molecular mechanism of cold resistance in banana

Abstract: Banana (Musa ssp.) is one of the most popular fruits in the world and the fourth largest food crop after rice, wheat and corn. It has become an important food and economic crop in sub-Saharan Afri-ca, South and Central America, and Asia. Bananas are originated from tropical regions, the main culti-vated bananas prefer high but do not low temperature, and are sensitive to cold stress. The optimum growth temperature for bananas is 24-32 ℃, and the growth will be blocked or even stagnated under 10-12 ℃. When the temperature drops to 1-2 ℃, the plants will suffer serious damage or even die.Therefore, low temperature is an important environmental factor affecting its planting area, growth de-velopment, yield and quality. Banana planting areas in China are mainly located in the southern subtrop-ical regions, including Guangdong, Fujian, Guangxi, Yunnan, Hainan and other provinces. Banana has become an important source of economy in our country’s southern subtropical regions and has played a key role in promoting rural economic development, agricultural efficiency, and farmers’income. How- ever, with global climate change, cold spells often occur during winter or early spring, which can have a serious impact on banana production, and restrict the healthy development of the banana industry. Culti-vating new cold-tolerant bananas has become one of the urgent problems in the development of banana industry in China. For a long time, triploids and extremely low fertility of most banana cultivars limit the improvement of cold-tolerant bananas through traditional breeding. Banana molecular breeding pro- vides an effective method for creating new banana germplasm with enhanced cold tolerance. The cold tolerance of banana germplasms is quite different. The main cultivated Cavendish banana (Musa AAA Group), which has a good flavor and taste, is cold-sensitive, but the relative germplasms such as Dajiao(Musa ABB Group) and Pisang Awak banana (Musa ABB group) are more tolerant to low temperatures of 0-4 ℃. These cold-tolerant banana varieties have become ideal genetic resources for digging out cold- tolerant genes of bananas themselves, improving cold- tolerant traits of bananas and cultivating new cold-tolerant germplasms. Therefore, studying the molecular mechanisms of different cold-tolerant banana varieties under cold stress is essential for digging out cold-tolerant genes for genetic manipula-tion. In recent years, with the further development of molecular biology technologies such as genomics and proteomics, especially the announcement of the banana genome sequence in 2012, the research on the molecular mechanism of banana cold tolerance has made great progress. In this review, we describe the different molecular mechanisms and regulatory networks of banana varieties from four different lev-els: biomembrane, phosphorylation signaling pathway, gene expression and protein expression. When the environment temperature becomes low, the biomembrane is the first part of cells to feel the changes of low temperature and is the most vulnerable to cold stress. Previous studies have shown that the cold tolerance of bananas is related to the lipid composition, ratio structure and membrane lipids of the bio- membrane. At the same time, related proteins on the membrane also play an important role in banana cold tolerance. For example, peroxidases MaPOD52 and MaPOD P7 participate in the membrane pro-tection by removing reactive oxygen species (ROS) to improve the cold tolerance of Dajiao; water chan-nels proteins MaPIP1;1, MaPIP2;4, MaPIP2;6b and MaTIP1;3 make Dajiao more cold-tolerant by main-taining leaf cell water potential. After the membrane is subjected to cold stress, the membrane fluidity will decrease. Ca2+ transporters located on the cell membrane or nuclear envelope will cause changes in the Ca2+ signal, resulting in the formation of a difference in calcium ion concentration inside and outside the membrane, which in turn induces cold-responsive gene expression. So far, reports on the mining and functional research on banana cold tolerance genes have been increasing year by year, and many func-tional genes related to banana cold tolerance have been identified. In this paper, according to the differences in gene expression of different cold-tolerant banana varieties under cold stress, a summary of banana cold-tolerance related genes are made. In addition, due to post-transcriptional regulation, there is little correlation between the transcription level of genes and their corresponding proteins. It is not pos-sible to directly infer the effect of cold stress on protein expression through changes in gene expression.Proteomics research focuses on all the genes encoded by the genome. Protein can not only supplement transcriptomics research, but also more directly reflect the signals and metabolic pathways related to ad-versity stress. But so far, there are relatively few studies on the difference in protein expression of ba-nanas under cold stress. We have summarized the results of previous studies. The information provided may help interested researchers cultivate cold-resistant bananas and improve cultivation measures. In addition, since plant response to cold stress is a very complex regulatory process, it is a quantitative trait controlled by multiple genes and is affected by many factors and conditions. In the future, we recommend using advanced scientific methods such as mass spectrometry and co-immunoprecipitation to deeply explore the interaction between multiple banana cold-tolerance genes and clarify their regulatory network, which will be crucial for analyzing the regulatory pathways of bananas in response to cold stress. It is very beneficial to the molecular breeding of banana cold tolerance in the future.