Plant Disease Control: Understanding the Roles of Toxins and Phytoalexins in Host-Pathogen Interaction

Naturally, plant habitats are exposed to several potential effects of biotic and different abiotic environmental challenges. Several types of micro-organisms namely; bacteria, viruses, fungi, nematodes, mites, insects, mammals and other herbivorous animals are found in large amounts in all ecosystems, which lead to considerable reduction in crop productivity. These organisms are agents carrying different diseases that can damage the plants through the secretion of toxic-microbial poisons that can penetrate in the plant tissues. Toxins are injurious substances that act on plant protoplast to influence disease development. In response to the stress effect, plants defend themselves by bearing some substances such as phytoalexins. Production of phytoalexins is one of the complex mechanisms through which plants exhibit disease resistance. Several findings specifically on phytoalexins have widen the understanding in the fields of plant biochemistry and molecular biology. However, this review reports the interaction of toxins and phytoalexins in plant-pathogen cycle, research progress on the association of phytoalexins with plant disease resistance as well as the role of the phytoalexins in plant disease control

The expression of target HSP70 gene and membrane stability determine heat tolerance in chili pepper

Experiments were carried out to study the mechanisms for heat tolerance in chili pepper (Capsicum annuum). To assess these mechanisms, six genotypes were evaluated for cellular membrane thermostability (CMT) and for HSP70 gene expression. The plants were grown in an experimental plant growth chamber. The mean value of CMT indicates that membrane integrity was not damaged by the high temperature treatment (50 °C) in most of the genotypes. The genotypes were classified as follows: heat-tolerant (greater than 60%), moderately tolerant (30% to 60%), and susceptible (less than 30%). The heat-tolerant plants recorded the highest CMTs at 89.27%, 88.03%, and 85.10% for AVPP0702, AVPP0116, and AVPP9905, respectively, which might be the reason for the change in their cell membrane thermostability. AVPP9703 and AVPP0002 showed CMTs of 15.87% and 18.43%, which might indicate their sensitivity to heat stress. Heat shock protein 70 kDa was identified and found to be differentially expressed under the heat stress. Under heat stress, significantly increased levels of the HSP70 gene were detected after 2 h of temperature treatment at 42 °C, which indicated that this gene is quickly and sharply induced by heat shock. This was true for all genotypes tested, which were significantly up-regulated by more than 36.9-, 7.10-, 3.87-, and 3-fold for AVPP0702, AVPP0116, AVPP0002, and AVPP9703, respectively. The HSP70 gene was found to be significantly down-regulated under heat stress in ‘Kulai’. AVPP0702, AVPP9905, and AVPP0116 could be considered as heat-tolerant genotypes, whereas ‘Kulai’ and AVPP9703 were found to be heat-sensitive genotypes in this investigation

Molecular analysis of Hsp70 mechanisms in plants and their function in response to stress

Studying the strategies of improving abiotic stress tolerance is quite imperative and research under this field will increase our understanding of response mechanisms to abiotic stress such as heat. The Hsp70 is an essential regulator of protein having the tendency to maintain internal cell stability like proper folding protein and breakdown of unfolded proteins. Hsp70 holds together protein substrates to help in movement, regulation, and prevent aggregation under physical and or chemical pressure. However, this review reports the molecular mechanism of heat shock protein 70 kDa (Hsp70) action and its structural and functional analysis, research progress on the interaction of Hsp70 with other proteins and their interaction mechanisms as well as the involvement of Hsp70 in abiotic stress responses as an adaptive defense mechanism

Identification of heat tolerant genotypes of chili pepper based on cell membrane thermostability and expression of heat shock protein genes

Terminal heat stress leads to change in the various parameters, such as heat shock protein genes and cell membrane thermostability, in chili pepper and is an important component of thermotolerance capacity. Experiments were carried out at Agrotechnology Unit, Agro Gene Bank and the Plant Physiology Laboratory, Institute of Tropical Agriculture, Universiti Putra Malaysia to study the mechanisms for heat tolerance in chili pepper genotypes. To assess these mechanisms, 36 genotypes were evaluated for morpho-physiological characters, cellular membrane thermostability (CMT) and for HSP70 gene expression. Significant (p <0.05) variation was observed among the genotypes for all the characters with genotypes AVPP9905 (1144.3 g) and Kulai (818.1 g) recording the highest yield per plant except chlorophyll content and days to flowering. The plants from selected chili pepper genotypes for CMT and HSP70 gene experiments were grown in experimental plant growth chamber for 4-8 weeks after sowing. The mean value of CMT indicates in most of the genotypes that membrane integrity was not damaged by the high temperature treatment (50ºC), with a mean value of 64.64%. The genotypes were classified based on heat tolerant (>60%), moderately tolerant (30%- 60%) and susceptible (<30%). Genotypes AVPP0702, AVPP0116 and AVPP9905 recorded the highest CMTs, at 89.27%, 89.27% and 85.10% respectively. AVPP9703 and AVPP0002 gave CMTs of 15.87% and 18.43%, respectively which might indicate their sensitivity to heat stress. HSP70 gene was identified and found differentially expressed under heat stress condition. Under heat stress, significantly increased levels of the HSP70 genes were detected after 2 hours temperature treatment at 42°C, which indicated these genes are quickly and sharply induced by heat shock. This was found especially true for all genotypes which were significantly up-regulated by more than 36.9, 7.10, 3.87 and 3 fold, for AVPP0702, AVPP0116, AVPP0002 and AVPP9703, respectively. Variety Kulai was found to be significantly down regulated under heat stress. Genotypes AVPP0702, AVPP9905 and AVPP0116 could be considered as heat tolerant genotypes while Kulai and AVPP9703 as heat sensitive genotypes from this study. The result further proves that CMT and HSP70 are key components of the defense mechanism against heat stress in chili pepper

Molecular confirmation of candidate Hsp70 gene associated with heat tolerance in BC3F2 advanced backcross lines and their phenotypic resemblance with recurrent chilli Kulai

Domestic production of chilli in Malaysia is insufficient which accounted for 52% self-sufficiency level. Poor performance of local varieties under high temperatures above 42°C is one of the major factors affecting chilli production. This study was conducted with the objective of introgress heat-tolerant gene (Hsps) from AVPP0702 donor into Kulai using marker-assisted backcrossing. A total of 68 SSR markers, including Hsp linked markers that showed polymorphism between the parents were used to assess the generation of backcrossing; BC1F1, BC2F1, BC3F1 and BC3F2 and the average RPG percentage of the recurrent parent was found to be 81, 90, 95 and 97%, respectively. The pattern of Hsp expression in the backcross generations was similar to the donor parent (upregulated with more than 4-fold increase). Twelve improved heat tolerant chilli lines were developed. Most of the morphological and agronomical traits were recovered in the selected improved heat-tolerant genotypes from Kulai such as plant height, number of days to 50% flowering, number of fruits, fruit length and total fruit yield per plant. Improved high-yielding heat-tolerant chilli lines showed tolerance to high temperature as well as did not express any negative effect on agronomic traits in comparison with Kulai variety

Analysis of recurrent parent genome recovery in marker-assisted backcross breeding program in watermelon

Marker–assisted backcross (MABC) is a breeding technique used to develop improved varieties by transferring a gene or QTL into the genome background of an elite variety after 2-3 generations. It is an advanced way of overcoming challenges facing conventional backcross methods as it speeds up the recurrent parent genome recovery (RPG). In order to develop a Fusarium wilt resistant watermelon variety, MABC was used to incorporate wilt resistant gene from the resistant inbred line CS-19 into the genome of the high yielding but wilt susceptible inbred line BL-14. There was estimation of RPG recovery in earlier generations with the use of polymorphic simple sequence repeat (SSR) markers. A total of 380 SSR markers were tested to identify polymorphism between the parents and 78 of them were found to be polymorphic. Background analysis revealed 74.7 – 94.4 and 86.6 – 96.8 % recovery in BC1F1 and BC2F1 generations, respectively. In the BC2F2 generation, RPG recovery ranged from 95.1 and 96.9 and the average in the selected lines was 96.14 %. This study led to the selection of plants that are similar to the recurrent parent and it showed the usefulness of MABC for the quick recovery of a parental genome in a backcrossing population

An Assessment of Ovarian Cancer Histotypes Across the African Diaspora

ObjectiveOvarian cancer in Black women is common in many West African countries but is relatively rare in North America. Black women have worse survival outcomes when compared to White women. Ovarian cancer histotype, diagnosis, and age at presentation are known prognostic factors for outcome. We sought to conduct a preliminary comparative assessment of these factors across the African diaspora. MethodsPatients diagnosed with ovarian cancer (all histologies) between June 2016-December 2019 in Departments of Pathology at 25 participating sites in Nigeria were identified. Comparative population-based data, inclusive of Caribbean-born Blacks (CBB) and US-born Blacks (USB), were additionally captured from the International Agency for Research on Cancer and Florida Cancer Data Systems. Histology, country of birth, and age at diagnosis data were collected and evaluated across the three subgroups: USB, CBB and Nigerians. Statistical analyses were done using chi-square and student's t-test with significance set at pResultsNigerians had the highest proportion of germ cell tumor (GCT, 11.5%) and sex-cord stromal (SCST, 16.2%) ovarian cancers relative to CBB and USB (p=0.001). CBB (79.4%) and USB (77.3%) women were diagnosed with a larger proportion of serous ovarian cancer than Nigerians (60.4%) (p<0.0001). Nigerians were diagnosed with epithelial ovarian cancers at the youngest age (51.7 +/- 12.8 years) relative to USB (58.9 +/- 15.0) and CBB (59.0 +/- 13.0,p<0.001). Black women [CBB (25.2 +/- 15.0), Nigerians (29.5 +/- 15.1), and USB (33.9 +/- 17.9)] were diagnosed with GCT younger than White women (35.4 +/- 20.5, p=0.011). Black women [Nigerians (47.5 +/- 15.9), USB (50.9 +/- 18.3) and CBB (50.9 +/- 18.3)] were also diagnosed with SCST younger than White women (55.6 +/- 16.5, p<0.01). ConclusionThere is significant variation in age of diagnosis and distribution of ovarian cancer histotype/diagnosis across the African diaspora. The etiology of these findings requires further investigation