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In an earlier greenhouse screening, we identified a local indica cultivar HT54 tolerant to high temperature at both seedling and grain-filling stages. In this study, we develop an optimized procedure for fine assessment of this heat tolerance. The results indicated that HT54 seedlings could tolerate high temperature up to 48 °C for 79h. The genetic analysis of F(1) and F(2) offspring derived from the cross between HT54 and HT13, a heat-sensitive breeding line, reveals that the heat tolerance of HT54 was controlled by a dominant major locus, which has been designated as OsHTAS (Oryza sativa heat tolerance at seedling stage). This locus was mapped on rice chromosome 9 within an interval of 420kb between markers of InDel5 and RM7364. The determined candidate ZFP gene has been confirmed to be cosegregated with a single nucleotide polymorphism (SNP) developed PCR-restriction fragment length polymorphism (RFLP) marker RBsp1407 in its promoter region. Another heat tolerance-associated SNP was identified in the first intron of its 5'-untranslated region. The existence of these SNPs thereby indicated that the OsHTAS locus contains at least two alleles. We named the one from HT54 as OsHTAS ( a ) and the one from HT13 as OsHTAS ( b ). Further dynamic expression analysis demonstrated that OsHTAS ( a ) was actively responsive to 45 °C high temperature stress compared with the OsHTAS ( b ) allele.

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Increasing evidence shows that improved nitrogen management can enhance lodging resistance and lower internodes play a key role in the lodging resistance of rice. However, little is known about the cellular and molecular mechanisms underlying the enhanced lodging resistance under improved nitrogen management. In the present study, two rice varieties, with contrasting lodging resistance, were grown under optimized N management (OPT) and farmers’ fertilizer practices. Under OPT, the lower internodes of both cultivars were shorter but the upper internodes were longer, while both culm diameter and wall thickness of lower internodes were dramatically increased. Microscopic examination showed that the culm wall of lower internodes under OPT contained more sclerenchyma cells beneath epidermis and vascular bundle sheath. The genome-wide gene expression profiling revealed that transcription of genes encoding cell wall loosening factors was down-regulated while transcription of genes participating in lignin and starch synthesis was up-regulated under OPT, resulting in inhibition of longitudinal growth, promotion in transverse growth of lower internodes and enhancement of lodging resistance. This is the first comprehensive report on the morpho-anatomical, mechanical, and molecular mechanisms of lodging resistance of rice under optimized N management.

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