Genome-wide association study of callus induction variation to explore the callus formation mechanism of rice

Rice(Oryza sativa) is one of the most widely cultivated food crops, worldwide. Tissue culture is extensively used in rice breeding and functional genome research. The ability to induce callus determines whether a particular rice variety can be subjected to tissue culture and Agrobacterium-mediated transformation. Over the past two decades, many quantitative trait loci(QTLs)related to callus induction traits have been identified;however, individual genes associated with rice callus induction have not been reported. In this study, we characterized three callus-induction traits in a global collection of 510 rice accessions. A genome-wide association study of the rice population in its entirety as well as subpopulations revealed 21 significant loci located in rice callus induction QTLs. We identified three candidate callus induction genes, namely CRL1, Os BMM1, and Os SET1, which Rese are orthologs of Arabidopsis LBD17/LBD29, BBM, and SWN,respectively, which are known to affect callus formation.Furthermore, we predicted that 14 candidate genes might be involved in rice callus induction and showed that RNA interference(RNAi)-mediated disruption of Os IAA10 inhibited callus formation on tissue culture medium.Embryo growth in the Os IAA10 RNAi line was not inhibited by synthetic auxin(2,4-D) treatment, suggesting that Os IAA10 may perceive auxin and activate the expression of downstream genes, such as CRL1, to induce callus formation. The significant loci and candidate genes identified here may provide insight into the mechanism underlying callus formation in rice.

Loss-of-function mutation of rice SLAC7 decreases chloroplast stability and induces a photoprotection mechanism in rice

Plants absorb sunlight to power the photochem- ical reactions of photosynthesis, which can potentially damage the photosynthetic machinery. However, the mech- anism that protects chloroplasts from the damage remains unclear. In this work, we demonstrated that rice （Oryza sativa L.） SLAC7 is a generally expressed membrane protein. Loss- of-function of SLAC7 caused continuous damage to the chloroplasts of mutant leaves under normal light conditions. Ion leakage indicators related to leaf damage such as H^O2 and abscisic acid levels were significantly higher in slac7-1 than in the wild type. Consistently, the photosynthesis efficiency and Fv/Fm ratio of slac7-1 were significantly decreased （similar to photoinhibition）. In response to chloroplast damage, slat7- 1 altered its leaf morphology （curled or fused leaf） by the synergy between plant hormones and transcriptional factors to decrease the absorption of light, suggesting that a photoprotection mechanism for chloroplast damage was activated in slac7-1. When grown in dark conditions, slac7-1 displayed a normal phenotype. 5LAC7 under the control of the AtSLAC1 promoter could partially complement thephenotypes of Arabidopsis slacl mutants, indicating a partial conservation of SLAC protein functions. These results suggest that SLAC7 is essential for maintaining the chloroplast stability in rice.