19 reported high temperature reducing the resistance of rice IRBB NILs carrying the Xa4 resistance gene to Xoo. Studying the effect of high temperature on the rice Xanthomonas oryzae pv. 18 reported that abiotic stress (drought) resulted in decrease of Xa4 R-gene mediated resistance to bacterial blight. 16, 17 showed that the reaction of resistance genes in rice to Magnaporthe grisea under high temperature depends on the genetic background of the rice genotype, where high temperature may either compromise resistance genes’ expression, or enhance the resistance response of gene Pi54. tomato ( Pst) strain DC3000 at 22 ☌ 14 and susceptible to the same strain at moderately elevated temperature between 27–30 ☌ 14, 15.
Similar reactions were reported in Arabidopsis, which shows resistance to virulent Pseudomonas syringae pv. Increased disease resistance to stripe rust ( Puccinia striiformis f.sp tritici) was observed in wheat under high temperature (25–35 ☌) and is likely caused by the significant expression of resistance gene Yr36, which is not effective under low temperature (15 ☌) 13, 14. High temperature affecting host resistance to pathogens has been reported in tobacco infected with Tobacco mosaic virus 12. Most studies on plant responses to environmental changes were carried out under single stress and are therefore unsuccessful in explaining plant responses to more than one stress factor 9. A small variation in temperature can affect plant growth, but also plants’ responses to pests and pathogens 10, 11. Temperature, water, relative humidity, light and circadian rhythm significantly influence plant defense and pathogen invasion 6.
According to these authors, the outcome of the interaction depends on the timing, nature and the severity of the stress. Unfortunately, due to their sessile lifestyle, plants have no chance to escape this environment (biotic and abiotic stresses) and must respond and adapt 6, 7, 8.Ībiotic stress may imply positive or negative effects on plant defense responses 7, 8, 9. Previous reports have shown that an increase of seasonal temperature by 1 ☌ results in a decline of major grains yield in the range of 2.5 to 16% in the tropics and subtropics 4, 5. This world population growth coupled with the impact of climate change on agricultural production in those countries demands a rapid growth in the food supply and animal feed, while conserving forest resources for climate mitigation 2, 3. The world population is projected to reach 9.7 billion by 2050 and half the world population growth is expected in developing countries 1. The interplay of both heat stress and Xoo responses as determined by up-regulated and down-regulated genes demonstrates how resistant plants cope with combined biotic and abiotic stresses. Interestingly, up-regulation of trehalose-6-phosphatase gene and low affinity cation transporter in IRBB67 suggest that IRBB67 maintained a certain homeostasis under high temperature which may have enhanced its resistance. Our findings highlight altered cellular compartments and point at a role of the cell wall involved in Xoo resistance and heat stress tolerance in both susceptible (IR24) and the resistant (IRBB67) NILs. Time course transcriptomic analysis revealed that temperature enhanced IRBB67 resistance to combined heat and Xoo. Moreover, Xa4 complements Xa7 resistance with no Xoo spread in planta beyond the symptomatic area under both temperature regimes in IRBB67. The pyramided line IRBB67 showed no differences in lesion length between both temperature regimes, demonstrating that non-effectiveness of Xa4 at high temperature did not affect IRBB67 resistance. Influence of high temperature on both R genes ( Xa4+Xa7) combined in IRBB67 was analyzed under growth chamber conditions and transcriptomic analysis performed. Recently, a reduced resistance in rice IRBB4 carrying Xa4, but an increase in resistance in IRBB7 carrying Xa7 resistance by increasing temperature has been reported. Increasing temperature often turns into inhibition of host plant defense to pathogens. In times of climate change, increasing temperatures are observed and further acceleration is expected worldwide. oryzae ( Xoo) implies substantial yield loss to rice. Rice bacterial blight (BB) caused by Xanthomonas oryzae pv.
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