Molecular and Physiological Responses of Rice and Weedy Rice to Heat and Drought Stress

Abstract

Rice is the staple food for about half of the world population. Rice grain yield and quality are affected by climatic changes. Arguably, rice cultivars’ genetic diversity is diminished from decades of breeding using narrow germplasm, requiring introgressions from other Oryza species, weedy or wild. Weedy rice has high genetic diversity, which is an essential resource for rice crop improvement. Here, we analyzed the phenotypic, physiological, and molecular profiles of two rice cultivars (IRGA 424 and SCS119 Rubi) and five weedy rice (WR), from five different Brazilian regions, in response to heat and drought stress. Drought and heat stress affected the phenotype and photosynthetic parameters in different ways in rice and WR genotypes. A WR from Northern Brazil yielded better under heat stress than the non-stressed check. Drought stress upregulated HSF7A while heat stress upregulated HSF2a. HSP74.8, HSP80.2, and HSP24.1 were upregulated in both conditions. Based on all evaluated traits, we hypothesized that in drought conditions increasing HSFA7 expression is related to tiller number and that increase WUE (water use efficiency) and HSFA2a expression are associated with yield. In heat conditions, Gs (stomatal conductance) and E’s increases may be related to plant height; tiller number is inversely associated with HSPs expression, and chlorophyll content and Ci (intercellular CO2 concentration) may be related to yield. Based on morphology, physiology, and gene regulation in heat and drought stress, we can discriminate genotypes that perform well under these stress conditions and utilize such genotypes as a source of genetic diversity for rice breeding.

The Role of Plant Growth-Promoting Bacteria in Alleviating the Adverse Effects of Drought on Plants

“…Many plants accumulate proline under unfavorable conditions, where proline concentrations in stress tolerant plants are higher than that in sensitive plants. In fact, plant mutants defective in proline production are more sensitive to drought [95]. Proline, as an osmolyte, stabilizes various components like proteins and membranes as well as scavenges reactive oxygen species (ROS) [2,14,17,19,47,92,93].…”

“…These hormones include abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA) and melatonin. Abscisic acid (ABA) is an important hormone in the plant response to drought [95,96], it is synthesized in plant roots and chloroplasts. Under drought stress, ABA cannot move through the plasma membrane but may be transported into the guard cells of stomata and induce stomatal closure.…”

“…ABA regulates osmotic balance and induces resistance to stresses via activating antioxidant genes such as catalase (CAT), superoxide dismutase (SOD) and peroxidase (POX) through ROS-induction, e.g., by increasing levels/activities of NADPH oxidase [98]. The pivotal role of ABA during drought was studied in several plant species like, e.g., rice (Oryza sativa) [85] and oilseed rape (Brassica napus) [95]. Similarly, drought stress causes an increase in the accumulation of another group of plant stress hormones, brassinosteroids that ultimately results in an increased water uptake, improved membrane stability and reduced ion leakage during drought conditions [99,100].…”

Impact of High Temperature Stress on Morpho Physiological Traits and Yield of Rice (Oryza sativa L.) Genotypes

“…CO 51 (14, 13 and 14) recorded more tiller numbers followed by Anna (R) 4 (13, 14 and 13) in ambient, ambient +2 o C and ambient +4 o C respectively (Table 2). Leonard et al (2021) reported that, almost all genotypes had reduced tiller numbers under heat stress. The panicle number is a yield component dependent on the tiller number.…”

“…With the rising temperature, plant height, and the number of tillers increased in rice (Oh-e et al, 2007). Leonard et al (2021) revealed that the number of tillers were decreased under hightemperature stress. Leaf area is an important parameter; higher leaf area contributes to higher chlorophyll content and photosynthesis, also increase grain yield.…”