Genome-wide identification of XTH gene family in Musa acuminata and response analyses of MaXTHs and xyloglucan to low temperature.

Banana (Musa spp.) production is seriously threatened by low temperature (LT) in tropical and subtropical regions. Xyloglucan endotransglycosylase/hydrolases (XTHs) are considered chief enzymes in cell wall remodelling and play a central role in stress responses. However, whether MaXTHs are involved in the low temperature stress tolerance in banana is not clear. Here, the identification and characterization of MaXTHs were carried out, followed by prediction of their cis-acting elements and protein-protein interactions. In addition, candidate MaXTHs involved in banana tolerance to LT were screened through a comparison of their responses to LT between tolerant and sensitive cultivars using RNA-Seq analysis. Moreover, immunofluorescence (IF) labelling was employed to compare changes in the temporal and spatial distribution of different types of xyloglucan components between these two cultivars upon stress. In total, 53 MaXTHs have been identified, and all were predicted to be located in the cell wall, 14 of them also in the cytoplasm. Only 11 MaXTHs have been found to interact with other proteins. Among 16 MaXTHs with LT responsiveness elements, MaXTH26/29/32/35/50 (Group I/II members) and MaXTH7/8 (Group IIIB members) might be involved in banana tolerance to LT stress. IF results suggested that the content of xyloglucan components recognized by CCRC-M87/103/104/106 antibodies might be negatively related to banana chilling tolerance. In conclusion, we have identified the MaXTH gene family and assessed cell wall re-modelling under LT stress. These results will be beneficial for banana breeding against stresses and enrich the cell wall-mediated resistance mechanism in plants to stresses.

Different responses of banana classical AGP genes and cell wall AGP components to low-temperature between chilling sensitive and tolerant cultivars.

KEY MESSAGE: Seventeen classical MaAGPs and 9 MbAGPs were identified and analyzed. MaAGP1/2/6/9/16/17, the antigens of JIM13 and LM2 antibodies are likely to be involved in banana chilling tolerance. Classical arabinogalactan proteins (AGPs) belong to glycosylphosphatidylinositol-anchored proteins, which are proved to be involved in signaling and cell wall metabolism upon stresses. However, rare information is available on the roles of classical AGPs in low temperature (LT) tolerance. Cultivation of banana in tropical and subtropical region is seriously threatened by LT stress. In the present study, 17 classical MaAGPs and nine MbAGPs in banana A and B genome were identified and characterized, respectively. Great diversity was present among different classical MaAGP/MbAGP members while five members (AGP3/6/11/13/14) showed 100% identity between these two gene families. We further investigated different responses of classical AGPs to LT between a chilling sensitive (CS) and tolerant (CT) banana cultivars. In addition, different changes in the temporal and spatial distribution of cell wall AGP components under LTs between these two cultivars were compared using immunofluorescence labeling. Seven classical MbAGPs were upregulated by LT(s) in the CT cultivar. Classical MaAGP4/6 was induced by LT(s) in both cultivars while MaAGP1/2/9/16/17 only in the CT cultivar. Moreover, these genes showed significantly higher transcription abundance in the CT cultivar than the CS one under LT(s) except classical MaAGP4. Similar results were observed with the epitopes of JIM13 and LM2 antibodies. The antigens of these antibodies and classical MaAGP1/2/6/9/16/17 might be related to LT tolerance of banana. These results provide additional information about plant classical AGPs and their involvement in LT tolerance, as well as their potential as candidate genes to be targeted when breeding CT banana.

Genome-wide analyses of banana fasciclin-like AGP genes and their differential expression under low-temperature stress in chilling sensitive and tolerant cultivars.

KEY MESSAGES: Thirty MaFLAs vary in their molecular features. MaFLA14/18/27/29 are likely to be involved in banana chilling tolerance by facilitating the cold signaling pathway and enhancing the cell wall biosynthesis. Although several studies have identified the molecular functions of individual fasciclin-like arabinogalactan protein (FLA) genes in plant growth and development, little information is available on their involvement in plant tolerance to low-temperature (LT) stress, and the related underlying mechanism is far from clear. In this study, the different expression of FLAs of banana (Musa acuminata) (MaFLAs) in the chilling-sensitive (CS) and chilling-tolerant (CT) banana cultivars under natural LT was investigated. Based on the latest banana genome database, a genome-wide identification of this gene family was done and the molecular features were analyzed. Thirty MaFLAs were distributed in 10 out of 11 chromosomes and these clustered into four major phylogenetic groups based on shared gene structure. Twenty-four MaFLAs contained N-terminal signal, 19 possessed predicted glycosylphosphatidylinositol (GPI), while 16 had both. Most MaFLAs were downregulated by LT stress. However, MaFLA14/18/29 were upregulated by LT in both cultivars with higher expression level recorded in the CT cultivar. Interestingly, MaFLA27 was significantly upregulated in the CT cultivar, but the opposite occurred for the CS cultivar. MaFLA27 possessed only N-terminal signal, MaFLA18 contained only GPI anchor, MaFLA29 possessed both, while MaFLA14 had neither. Thus, it was suggested that the accumulation of these FLAs in banana under LT could improve banana chilling tolerance through facilitating cold signal pathway and thereafter enhancing biosynthesis of plant cell wall components. The results provide background information of MaFLAs, suggest their involvement in plant chilling tolerance and their potential as candidate genes to be targeted when breeding CT banana.