| ||||||||||||||||||||
Waterproof genes?
Mention of rice cultivation will lead many to picture paddy fields with the rice plants rooted under water. Indeed, many rice varieties are grown in this way but there are also flood-intolerant varieties, while even paddy rice is vulnerable to total submergence. The main factor in flooding is O2 deprivation, and it is of great interest to understand the mechanisms involved in toleration of hypoxia. One approach to this is to investigate the array of genes activated during O2 deprivation, as reported extensively by Agarwal and Grover (University of Delhi, India, pp. 831–844). At the heart of the methodology was the construction of ‘subtraction’ cDNA libraries, which enabled a comparison between flood-tolerant (variety FR13A) plants exposed to control conditions or to O2 deprivation and, secondly, comparison between the responses of FR13A with those of a flood-intolerant variety, PB1. These libraries were then used in expression profiling, using reverse Northern analysis, which identified specifically the cDNA clones, 293 in all, that represented genes up-regulated in FR13A during O2 deprivation. Partial sequencing of these clones then provided the same number of ESTs (expressed sequence tags). It is a major advantage for this work that the rice genome has been sequenced and this has enabled the authors to make at least a partial identification of the up-regulated genes. The detail lies outside the scope of this commentary; here we focus on the overall classification of these genes. The largest group, representing 68 % of the transcripts, are as yet ‘anonymous’ within the rice genome. The remaining 32 % may be grouped into six categories, which, starting from the largest category, are N and C metabolism (including the electron transport chain), transport, RNA binding and recognition, transcription factors, signalling pathways and anti-oxidant metabolism. This is a great start to understanding the molecular biology of flood tolerance in rice and bodes well for future breeding or gene transfer programmes.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
| ||||||||||||||||||||