Effects of gibberellin priming on seedling emergence and transcripts involved in mesocotyl elongation in rice under deep direct-seeding conditions

Mesocotyl elongation is a key trait influencing seedling emergence and establishment in direct-seeding rice cultivation.The phytohormone gibberellin(GA)has positive effects on mesocotyl elongation in rice.However,the physiological and molecular basis underlying the regulation of mesocotyl elongation mediated by GA priming under deep-sowing conditions remains largely unclear.In the present study,we performed a physiological and comprehensive transcriptomic analysis of the function of GA priming in mesocotyl elongation and seedling emergence using a direct-seeding japonica rice cultivar ZH10 at a5-cm sowing depth.Physiological experiments indicated that GA priming significantly improved rice seedling emergence by increasing the activity of starch-metabolizing enzymes and compatible solute content to supply the energy essential for subsequent development.Transcriptomic analysis revealed 7074 differentially expressed genes(false discovery rate of<0.05,|log2(fold change)|of≥1)after GA priming.Furthermore,gene ontology(GO)and Kyoto encyclopedia of genes and genomes(KEGG)enrichment analyses revealed that genes associated with transcriptional regulation,plant hormone biosynthesis or signaling,and starch and sucrose metabolism were critical for GA-mediated promotion of rice mesocotyl elongation.Further analyses showed that the expression of the transcription factor(TF)genes(v-myb avian myeloblastosis viral oncogene homolog(MYB)alternative splicing 1(MYBAS1),phytochrome-interacting factors 1(PIF1),Oryza sativa teosinte branched 1/cycloidea/proliferating cell factor 5(Os TCP5),slender 1(SLN1),and mini zinc finger 1(MIF1)),plant hormone biosynthesis or signaling genes(brassinazole-resistant 1(BZR1),ent-kaurenoic acid oxidase-like(KAO),GRETCHEN HAGEN 3.2(GH3.2),and small auxin up RNA 36(SAUR36)),and starch and sucrose metabolism genes(α-amylases(AMY2 A and AMY1.4))was highly correlated with the mesocotyl elongation and deep-sowing tolerance response.These results enhance our understanding of how nutrient metabolism-related substances and genes regulate rice mesocotyl elongation.This may facilitate future studies on related genes and the development of novel rice varieties tolerant to deep sowing.

OsNAC5 orchestrates OsABI5 to fine-tune cold tolerance in rice

Due to its tropical origins,rice(Oryza sativa)is susceptible to cold stress,which poses severe threats to production.OsNAC5,a NAC-type transcription factor,participates in the cold stress response of rice,but the detailed mechanisms remain poorly understood.Here,we demonstrate that OsNAC5 positively regulates cold tolerance at germination and in seedlings by directly activating the expression of ABSCISIC ACID INSENSITIVE 5(OsABI5).Haplotype analysis indicated that single nucleotide polymorphisms in a NAC-binding site in the OsABI5 promoter are strongly associated with cold tolerance.OsNAC5 also enhanced OsABI5 stability,thus regulating the expression of cold-responsive(COR)genes,enabling fine-tuned control of OsABI5 action for rapid,precise plant responses to cold stress.DNA affinity purification sequencing coupled with transcriptome deep sequencing identified several OsABI5 target genes involved in COR expression,including DEHYDRATION-RESPONSIVE ELEMENT BINDING FACTOR 1A(OsDREB1A),OsMYB20,and PEROXIDASE 70(OsPRX70).In vivo and in vitro analyses suggested that OsABI5 positively regulates COR gene transcription,with marked COR upregulation in OsNAC5-overexpressing lines and downregulation in osnac5 and/or osabi5 knockout mutants.This study extends our understanding of cold tolerance regulation via OsNAC5 through the OsABI5-CORs transcription module,which may be used to ameliorate cold tolerance in rice via advanced breeding.

Melatonin activates the OsbZIP79–OsABI5 module that orchestrates nitrogen and ROS homeostasis to alleviate nitrogen-limitation stress in rice

Melatonin(Mel)has previously been reported to effectively alleviate nitrogen-limitation(N-L)stress and thus increase nitrogen-use efficiency(NUE)in several plants,but the underlying mechanism remains obscure.Here,we revealed that OsbZIP79(BASIC LEUCINE ZIPPER 79)is transcriptionally activated under N-L conditions,and its expression is further enhanced by exogenous Mel.By the combined use of omics,genetics,and biological techniques,we revealed that the OsbZIP79–OsABI5(ABSCISIC ACID INSENSITIVE 5)module stimulated regulation of reactive oxygen species(ROS)homeostasis and the uptake and metabolismof nitrogen under conditions of indoor nitrogen limitation(1/16 normal level).OsbZIP79 activated the transcription of OsABI5,and OsABI5 then bound to the promoters of target genes,including genes involved in ROS homeostasis and nitrogen metabolism,activating their transcription.This module was also indispensable for upregulation of several other genes involved in abscisic acid catabolism,nitrogen uptake,and assimilation under N-L and Mel treatment,although these genes were not directly transactivated by OsABI5.Field experiments demonstrated that Mel significantly improved rice growth under low nitrogen(L-N,half the normal level)by the same mechanism revealed in the nitrogen-limitation study.Mel application produced a 28.6%yield increase under L-N and thus similar increases in NUE.Also,two OsbZIP79-overexpression lines grown in L-N field plots had significantly higher NUE(+13.7%and+21.2%)than their wild types.Together,our data show that an OsbZIP79–OsABI5 module regulates the rice response to N insufficiency(N limitation or low N),which is important for increasing NUE in rice production.