No abstract

Expansin is a cell wall loosening protein without hydrolytic activity, which allows cell expansion by influencing cell wall extensibility. Previous studies showed that the suppression of expansin genes (EXPA1, EXPA3, EXPA5 and EXPA10) resulted in defective organ growth and altered cell wall chemical composition [1,2]. However, the molecular mechanism on how the suppression of non-enzymatic expansin expression can result in widespread effects on plant cell wall and organ growth is still unclear. In this study, we performed transcriptomic analysis on the hypocotyls of previously reported transgenic Arabidopsis line [1] to investigate the effects of expansin gene suppression on the global gene expression pattern, particularly on the cell wall related genes.

Expansin increases cell wall extensibility to allow cell wall loosening and cell expansion even in the absence of hydrolytic activity. Previous studies showed that excessive overexpression of expansin gene resulted in defective growth (Goh et al., 2014; Rochange et al., 2001) [1,2] and altered cell wall chemical composition (Zenoni et al., 2011) [3]. However, the molecular mechanism on how the overexpression of non-enzymatic cell wall protein expansin can result in widespread effects on plant cell wall and organ growth remains unclear. We acquired transcriptomic data on previously reported transgenic Arabidopsis line (Goh et al., 2014) [1] to investigate the effects of overexpressing a heterologus cucumber expansin gene (CsEXPA1) on the global gene expression pattern during early and late phases of etiolated hypocotyl growth.

Local drought-tolerant rice variety MR303 (Oryza sativa spp. Indica) has higher tolerance towards abiotic stress while maintaining its high yield and grain quality. Expression of OsWRKY11 has shown to be a positive modulator while OsNAC2 is a negative modulator for drought-tolerance in Oryza sativa spp. Japonica. However, these transcription factor (TF) genes regulation are species-specific and its regulation may differ in our local rice variety. Thus, our study aimed to identify the relative expression of these genes and its effects on plant morphology and drought-tolerance capabilities. Our results on relative expression of OsWRKY11 in the MR303 rice variety showed that under drought stress, this gene was highly expressed. This result was similar to previous findings in Oryza sativa spp. Japonica. However, for OsNAC2 gene expression, our results contradict with previous findings where under drought stress, this gene was also highly expressed instead of downregulated. These results suggest that our local rice variety may have different gene regulation under drought stress compared to other rice varieties. Proline assay showed that proline contents in drought-treated plant has increased 10 times compared to control which associated with drought-tolerance activities. Further studies may be conducted to gain better understanding on the roles of these genes in regulating drought-responsive genes in the local variety.