MaHsf24, a novel negative modulator, regulates cold tolerance in banana fruits by repressing the expression of HSPs and antioxidant enzyme genes.

Transcriptional regulation mechanisms underlying chilling injury (CI) development have been widely investigated in model plants and cold-sensitive fruits, such as banana (Musa acuminata). However, unlike the well-known NAC and WRKY transcription factors (TFs), the function and deciphering mechanism of heat shock factors (HSFs) involving in cold response are still fragmented. Here, we showed that hot water treatment (HWT) alleviated CI in harvested banana fruits accomplishing with reduced reactive oxygen species (ROS) accumulation and increased antioxidant enzyme activities. A cold-inducible but HWT-inhibited HSF, MaHsf24, was identified. Using DNA affinity purification sequencing (DAP-seq) combined with RNA-seq analyses, we found three heat shock protein (HSP) genes (MaHSP23.6, MaHSP70-1.1 and MaHSP70-1.2) and three antioxidant enzyme genes (MaAPX1, MaMDAR4 and MaGSTZ1) were the potential targets of MaHsf24. Subsequent electrophoretic mobility shift assay (EMSA), chromatin immunoprecipitation coupled with quantitative PCR (ChIP-qPCR) and dual-luciferase reporter (DLR) analyses demonstrated that MaHsf24 repressed the transcription of these six targets via directly binding to their promoters. Moreover, stably overexpressing MaHsf24 in tomatoes increased cold sensitivity by suppressing the expressions of HSPs and antioxidant enzyme genes, while HWT could recover cold tolerance, maintaining higher levels of HSPs and antioxidant enzyme genes, and activities of antioxidant enzymes. In contrast, transiently silencing MaHsf24 by virus-induced gene silencing (VIGS) in banana peels conferred cold resistance with the upregulation of MaHSPs and antioxidant enzyme genes. Collectively, our findings support the negative role of MaHsf24 in cold tolerance, and unravel a novel regulatory network controlling bananas CI occurrence, concerning MaHsf24-exerted inhibition of MaHSPs and antioxidant enzyme genes.

Overexpression of MaTPD1A impairs fruit and pollen development by modulating some regulators in Musa itinerans.

BACKGROUND: Pollen formation and development is important for crop fertility and is a key factor for hybrid development. Previous reports have indicated that Arabidopsis thaliana TAPETUM DETERMINANT1 (AtTPD1) and its rice (Oryza sativa) homolog, OsTPD1-like (OsTDL1A), are required for cell specialization and greatly affect pollen formation and development. Little is known about the role of the TPD1 homolog in banana pollen development. RESULTS: Here, we report the identification and characterization of TPD1 homologs in diploid banana (Musa itinerans) and examine their role in pollen development by overexpressing the closest homolog, MaTPD1A. MaTPD1A exhibits high expression in stamen and localizes in the plasma membrane. MaTPD1A-overexpressing plants produce no pollen grains and smaller and seedless fruit compared to wild-type plants. Transcriptome analysis showed that in plant hormone, starch and sucrose metabolism, and linolenic acid metabolism-related pathways were affected by overexpression of MaTPD1A, and the expression of several key regulators, such as PTC1 and MYB80, which are known to affect anther development, is affected in MaTPD1A-overexpressing lines. CONCLUSIONS: Our results indicate that MaTPD1A plays an important role in pollen formation and fruit development in diploid banana, possibly by affecting the expression of some key regulators of pollen development.

Assessment of External Properties for Identifying Banana Fruit Maturity Stages Using Optical Imaging Techniques.

The maturity stage of bananas has a considerable influence on the fruit postharvest quality and the shelf life. In this study, an optical imaging based method was formulated to assess the importance of different external properties on the identification of four successive banana maturity stages. External optical properties, including the peel color and the local textural and local shape information, were extracted from the stalk, middle and tip of the bananas. Specifically, the peel color attributes were calculated from individual channels in the hue-saturation-value (HSV), the International Commission on Illumination (CIE) L*a*b* and the CIE L*ch color spaces; the textural information was encoded using a local binary pattern with uniform patterns (UP-LBP); and the local shape features were described by histogram of oriented gradients (HOG). Three classifiers based on the naïve Bayes (NB), linear discriminant analysis (LDA) and support vector machine (SVM) algorithms were adopted to evaluate the performance of identifying banana fruit maturity stages using the different optical appearance features. The experimental results demonstrate that overall identification accuracies of 99.2%, 100% and 99.2% were achieved using color appearance features with the NB, LDA and SVM classifiers, respectively; overall accuracies of 92.6%, 86.8% and 93.4% were obtained using local textural features for the three classifiers, respectively; and overall accuracies of only 84.3%, 83.5% and 82.6% were obtained using local shape features with the three classifiers, respectively. Compared to the complicated calculation of both the local textural and local shape properties, the simplicity and high accuracy of the peel color property make it more appropriate for identifying banana fruit maturity stages using optical imaging techniques.

Fusarium musae infected banana fruits as potential source of human fusariosis: May occur more frequently than we might think and hypotheses about infection.

The banana fruit infecting fungus Fusarium musae was originally known as a distinct population within Fusarium verticillioides. However, recently, Fusarium musae was installed as a separate species and the first cases of human infection associated with Fusarium musae were found. In this article, we report an additional survey indicating that human pathogenic Fusarium musae infections may occur more frequently than we might think. Moreover, we evaluate the hypotheses on how infection can be acquired. A first hypothesis is that banana fruits act as carriers of Fusarium musae spores and thereby be the source of human infection with Fusarium musae. Acquisition is likely to be caused through contact with Fusarium musae contaminated banana fruits, either being imported or after traveling of the patient to a banana-producing country. An alternative hypothesis is that Fusarium musae is not only present on banana fruits, but also on other plant hosts or environmental sources.

Toxigenic profiles and trinucleotide repeat diversity of Fusarium species isolated from banana fruits.

Infesting Fusarium species isolated from banana fruit samples were identified and quantified by morphological, mycotoxicological and molecular tools. A total of 19 Fusarium isolates were obtained: F. semitectum was most predominant (26%), followed by F. proliferatum (16%), F. circinatum (16%), F. chlamydosporum (10.5%), F. solani (10.5%), F. oxysporum (10.5%) and F. thapsinum (5%). Fumonisin B1, deoxynivalenol and zearalenone contents were assayed by high-performance liquid chromatography (HPLC). Seventeen isolates, belonging to F. chlamydosporum, F. circinatum, F. semitectum, F. solani, F. thapsinum, F. proliferatum and Fusarium spp., produced mycotoxins when cultured on rice medium. Fumonisin was produced by all of the studied Fusarium isolates, except F. oxysporum, at a concentration of over 1 µg/mL. F. citrinium isolates 4 and 5 and F. solani isolate 3 were the most potent producers of deoxynivalenol. We compared the 19 Fusarium isolates based on the bands amplified by 10 microsatellite primers. Of these, seven primers, (TCC)5, (TGG)5, (GTA)5, (ATG)5, (TAC)5, (TGC)5 and (TGT)5, yielded a high number of bands and different mean number of alleles. The similarity level between isolates was calculated using a simple matching coefficient. Dendrograms were constructed by the unweighted pair-group method with arithmetical averages (UPGMA). Two main clusters were observed. The interspecific genetic similarity between Fusarium spp. isolates was between 40% and 58% and the intraspecific similarity from 58% to 100%, indicating a high degree of genetic diversity in the tested isolates. Some unexpected genetic similarities were observed among the isolates, indicating non-agreement between morphological and molecular identification of the isolates.