Evaluation of seven function-known candidate genes for their effects on improving drought resistance of transgenic rice under field conditions.

Many stress responsive genes have been reported with an effect on improving stress resistance in model plants under greenhouse conditions. Towards identification of genes for drought resistance breeding, seven well documented genes (CBF3, SOS2, NCED2, NPK1, LOS5, ZAT10, and NHX1) in stress resistance were selected in this study and transformed into rice cultivar Zhonghua 11 under the control of constitutive promoter Actin1 and stress-inducible promoter of a rice HVA22 homolog, and transgenic rice were tested for drought resistance under field conditions. A total of 1598 independent transgenic T0 plants were generated. The percentages of single copy and expression of the transgenes were 36.7% and 57.6%, respectively. For each gene construct, 30 T1 families with expression of transgene were selected for drought resistance testing at the reproductive stage in field, and 10 of them were tested in PVC pipes with a defined stress protocol at the same stage. Relative yield and relative spikelet fertility were used as two major criteria to evaluate drought resistance performance because significantly decreased yield was observed in the T1 generation. Transgenic families of eight constructs (HVA22P:CBF3, HVA22P:NPK1, Actin1:LOS5, HVA22P:LOS5, Actin1:ZAT10, HVA22P:ZAT10, Actin1:NHX1, and HVA22P:NHX1) showed significantly higher RY than wild-type (WT) under both drought stress field and PVC tube conditions. Transgenic families of 9 constructs (HVA22P:SOS2 and CBF3, LOS5, ZAT10, and NHX1 by both promoters) showed significantly higher relative spikelet fertility than WT in the field or PVC pipes. In the field drought resistance testing of T2 families derived from the T1 families with relatively lower yield decrease, transgenic families of seven constructs (HVA22P:CBF3, Actin1:NPK1, HVA22P:NPK1, Actin1:LOS5, HVA22P:LOS5, Actin1:ZAT10, and HVA22P:ZAT10) showed significantly higher yield per plant than WT, and families of nine constructs (Actin1:CBF3, HVA22P:CBF3, HVA22P:SOS2, HVA22P:NPK1, Actin1:LOS5, HVA22P:LOS5, Actin1:ZAT10, HVA22P:ZAT10, and Actin1:NHX1) had higher spikelet fertility than WT. In general, LOS5 and ZAT10 showed relatively better effect than the other five genes in improving drought resistance of transgenic rice under field conditions. The results and experience obtained from this study could be a useful reference for drought resistance engineering in rice.

Isolation and identification of SA and JA inducible protein kinase gene OsSJMK1 in rice.

On the basis of a JA-inducible EST, the full length cDNA of a putative protein kinase gene, OsSJMKJ, was isolated from rice (Oryza sativa L.). The predicted protein of this gene, consisting of 498 amino acids with a predicted PI value of 8.43, contains a mitogen-activated protein kinase (MAPK) domain with a dual-phosphorylation activation motif TDY (Thr-Asp-Tyr) and a C-terminus domain that feature a typical MAPK belonging to subgroup V. OsSJMK1 showed 81% sequence identity to the reported BWMK1, a blast fungus and wounding inducible protein, in the N-terminus kinase domain but had low sequence identity in the C-terminus domain. Despite the high similarity of gene structure between OsSJMK1 and BWMK1, the expression of OsSJMK1 was weakly induced by blast fungus but not wounding, rather it was transiently induced by jasmonic acid (JA) and salicylic acid (SA) at early stages of treatment. This gene was not induced by other hormones (such as ABA) or abiotic stresses, such as drought and salinity. The low level of transcript of this gene was detected in the various tissues of rice. The results suggest that OsSJMK1 might be activated specifically by JA and SA and involved in defense signaling pathways.

Identification of quantitative trait loci for ABA sensitivity at seed germination and seedling stages in rice.

Abscisic acid (ABA) is one of the important plant hormones, which plays a critical role in seed development and adaptation to abiotic stresses. The sensitivity of rice (Oryza sativa L.) to exogenous ABA at seed germination and seedling stages was investigated in the recombinant inbred line (RIL) population derived from a cross between irrigated rice Zhenshan 97 and upland rice IRAT109, using relative germination vigor (RGV), relative germination rate (RGR) and leaf rolling scores of spraying (LRS) or culturing (LRC) with ABA as sensitivity indexes. The phenotypic correlation analysis revealed that only RGV at germination stage was positively correlated to ABA sensitivity at seedling stage. QTL detection using composite interval mapping (CIM) and mixed linear model was conducted to dissect the genetic basis of ABA sensitivity, and the single-locus QTLs detected by both methods are in good agreement with each other. Five single QTLs and six pairs of epistatic QTLs were detected for ABA sensitivity at germination stage. Eight single QTLs and five pairs of epistatic QTLs were detected for ABA sensitivity at seedling stage. Two QTLs were common between LRS and LRC; and one common QTL was detected for RGV, LRS and LRC simultaneously. These results indicated that both single and epistatic loci were involved in the ABA sensitivity in rice, and the genetic basis of ABA sensitivity at seed germination and seedling stage was largely different.