Molecular mechanisms of salinity tolerance in rice

Salinity is one of the major abiotic stresses which impose constraints to plant growth and production.Rice(Oryza sativa L.)is one of the most important staple food crops and a model monocot plant.Its production is expanding into regions that are affected by soil salinity,requiring cultivars more tolerant to saline conditions.Understanding the molecular mechanisms of such tolerance could lay a foundation for varietal improvement of salt tolerance in rice.In spite of extensive studies exploring the mechanism of salt tolerance,there has been limited progress in breeding for increased salinity tolerance.In this review,we summarize the information about the major molecular mechanisms underlying salinity tolerance in rice and further discuss the limitations in breeding for salinity tolerance.We show that numerous gene families and interaction networks are involved in the regulation of rice responses to salinity,prompting a need for a comprehensive functional analysis.We also show that most studies are based on whole-plant level analyses with only a few reports focused on tissue-and/or cell-specific gene expression.More details of salt-responsive channel and transporter activities at tissue-and cell-specific level still need to be documented before these traits can be incorporated into elite rice germplasm.Thus,future studies should focus on diversity of available genetic resources and,particular,wild rice relatives,to reincorporate salinity tolerance traits lost during domestication.

Diversity of Sodium Transporter HKT1;5 in Genus Oryza

Asian cultivated rice shows allelic variation in sodium transporter,OsHKT1;5,correlating with shoot sodium exclusion(salinity tolerance).These changes map to intra/extracellularly-oriented loops that occur between four transmembrane-P loop-transmembrane(MPM)motifs in OsHKT1;5.HKT1;5 sequences from more recently evolved Oryza species(O.sativa/O.officinalis complex species)contain two expansions that involve two intracellularly oriented loops/helical regions between MPM domains,potentially governing transport characteristics,while more ancestral HKT1;5 sequences have shorter intracellular loops.We compared homology models for homoeologous OcHKT 1;5-K and OcHKT1;5-L from halophytic O.coarctata to identify complementary amino acid residues in OcHKT1;5-L that potentially enhance affinity for Na+.Using haplotyping,we showed that Asian cultivated rice accessions only have a fraction of HKT1;5 diversity available in progenitor wild rice species(O.nivara and O.rufipogon).Progenitor HKT1;5 haplotypes can thus be used as novel potential donors for enhancing cultivated rice salinity tolerance.Within Asian rice accessions,10 non-synonymous HKT1;5 haplotypic groups occur.More HKT1;5 haplotypic diversities occur in cultivated indica gene pool compared to japonica.Predominant Haplotypes 2 and 10 occur in mutually exclusive japonica and indica groups,corresponding to haplotypes in O.sativa salt-sensitive and salt-tolerant landraces,respectively.This distinct haplotype partitioning may have originated in separate ancestral gene pools of indica and japonica,or from different haplotypes selected during domestication.Predominance of specific HKT1;5 haplotypes within the 3000 rice dataset may relate to eco-physiological fitness in specific geo-climatic and/or edaphic contexts.

Polycystic Ovarian Syndrome (PCOS): Exploring Its Impact on Obstetrical Outcomes

Polycystic ovarian syndrome (PCOS) disrupts ovulation leading to both infertility and miscarriage;yet, its impact on obstetrical outcomes remains largely uncertain due to conflicting findings. We analyzed data from the CDC Pregnancy Risk Assessment of Monitoring System, specifically Standard Core and Phase 8 responses, with 9549 respondents across the United States through SPSS 28 software in this cross-sectional study. Two variables assessed PCOS status in respondents: history of PCOS and PCOS during pregnancy. With a history of PCOS, there were significantly increased odds of diabetic (OR 1.665, p < 0.001), hypertensive disorders (OR 1.589, p < 0.001) during pregnancy, neonatal mortality (OR 1.550, p < 0.001), cesarean section (C/S) (OR 1.489, p < 0.001), and preterm prelabor rupture of membranes (PPROM) (OR 2.081, p < 0.001). With PCOS diagnosed during pregnancy, there were significantly greater odds of diabetes (OR 3.278, p < 0.001), hypertensive disorders (OR 2.935, p < 0.001) during pregnancy, and significantly decreased risk for small for gestational age (2 standard deviations) (OR 0.337, p = 0.024). PCOS is a significant risk factor that contributes to maternal morbidity. Our results support the hypothesis that PCOS’ impact extends well into a woman’s obstetrical journey, with varying degrees of associated adverse maternal and fetal risks. Preliminary pathophysiologic explanations associated with PCOS gestational diabetes include pre-existing insulin resistance. Meanwhile, altered placentation and endovascular changes associated with PCOS secondary to a baseline deranged metabolic environment predispose patients to developing hypertensive disorders, PPROM, and preterm delivery. Associations between neonatal mortality and C/S can be attributed to elevated maternal body mass index. The pathophysiologic link between PCOS and the above obstetrical outcomes still remains unknown, necessitating further investigation;however, this study identifies the outcomes that require the most attention at this time.

Proto Kranz-like leaf traits and cellular ionic regulation are associated with salinity tolerance in a halophytic wild rice

Species of wild rice(Oryza spp.)possess a wide range of stress tolerance traits that can be potentially utilized in breeding climate-resilient cultivated rice cultivars(Oryza sativa)thereby aiding global food security.In this study,we conducted a greenhouse trial to evaluate the salinity tolerance of six wild rice species,one cultivated rice cultivar(IR64)and one landrace(Pokkali)using a range of electrophysiological,imaging,and whole-plant physiological techniques.Three wild species(O.latifolia,O.officinalis and O.coarctata)were found to possess superior salinity stress tolerance.The underlying mechanisms,however,were strikingly different.Na+accumulation in leaves of O.latifolia,O.officinalis and O.coarctata were significantly higher than the tolerant landrace,Pokkali.Na+accumulation in mesophyll cells was only observed in O.coarctata,suggesting that O.officinalis and O.latifolia avoid Na+accumulation in mesophyll by allocating Na+to other parts of the leaf.The finding also suggests that O.coarctata might be able to employ Na+as osmolyte without affecting its growth.Further study of Na+allocation in leaves will be helpful to understand the mechanisms of Na+accumulation in these species.In addition,O.coarctata showed Proto Kranz-like leaf anatomy(enlarged bundle sheath cells and lower numbers of mesophyll cells),and higher expression of C4-related genes(e.g.,NADPME,PPDK)and was a clear outlier with respect to salinity tolerance among the studied wild and cultivated Oryza species.The unique phylogenetic relationship of O.coarctata with C4 grasses suggests the potential of this species for breeding rice with high photosynthetic rate under salinity stress in the future.