Analysis of Stress-Responsive Gene Expression in Cultivated and Weedy Rice Differing in Cold Stress Tolerance

Abstract

Rice (Oryza sativa L.) cultivars show impairment of growth in response to environmental stresses such as cold at the early seedling stage. Locally adapted weedy rice is able to survive under adverse environmental conditions, and can emerge in fields from greater soil depth. Cold-tolerant weedy rice can be a good genetic source for developing cold-tolerant, weed-competitive rice cultivars. An in-depth analysis is presented here of diverse indica and japonica rice genotypes, mostly weedy rice, for cold stress response to provide an understanding of different stress adaptive mechanisms towards improvement of the rice crop performance in the field. We have tested a collection of weedy rice genotypes to: 1) classify the subspecies (ssp.) grouping (japonica or indica) of 21 accessions; 2) evaluate their sensitivity to cold stress; and 3) analyze the expression of stress-responsive genes under cold stress and a combination of cold and depth stress. Seeds were germinated at 25°C at 1.5- and 10-cm sowing depth for 10d. Seedlings were then exposed to cold stress at 10°C for 6, 24 and 96h, and the expression of cold-, anoxia-, and submergence-inducible genes was analyzed. Control plants were seeded at 1.5cm depth and kept at 25°C. The analysis revealed that cold stress signaling in indica genotypes is more complex than that of japonica as it operates via both the CBF-dependent and CBF-independent pathways, implicated through induction of transcription factors including OsNAC2, OsMYB46 and OsF-BOX28. When plants were exposed to cold + sowing depth stress, a complex signaling network was induced that involved cross talk between stresses mediated by CBF-dependent and CBF-independent pathways to circumvent the detrimental effects of stresses. The experiments revealed the importance of the CBF regulon for tolerance to both stresses in japonica and indica ssp. The mechanisms for cold tolerance differed among weedy indica genotypes and also between weedy indica and cultivated japonica ssp. as indicated by the up/downregulation of various stress-responsive pathways identified from gene expression analysis. The cold-stress response is described in relation to the stress signaling pathways, showing complex adaptive mechanisms in different genotypes.

Overexpression of Rice Expansin7 (Osexpa7) Confers Enhanced Tolerance to Salt Stress in Rice

“…The involvement of some expansin family genes in the abiotic stress response and plant development has been reported in rice. OsEXPA3 was shown to be induced in response to salt stress [39], and OsEXPA7 accumulated under cold stress [41]. OsEXPA7, OsEXPA4, and OsEXPA2 have been reported to be upregulated before internode elongation under submergence [40,60].…”

“…Furthermore, under submergence conditions, OsEXPA2 and OsEXPA7 are upregulated and are likely to be involved in rice coleoptile elongation [40]. OsEXPA7 has been shown to be accumulated under cold stress [41]. Although expansins have been known to respond to abiotic stress in various species, few studies have examined their function in rice.…”

Weedy rice in sustainable rice production. A review

“…Rice cultivars do not usually emerge well from greater soil depths, whereas the weedy ecotypes can emerge from deeper soil profiles (Teekachunhatean 1985;Bevilacqua et al 2015). Weedy rice seeds have been recorded to emerge from 13 cm of soil.…”

The 21st Century Agriculture: When Rice Research Draws Attention to Climate Variability and How Weedy Rice and Underutilized Grains Come in Handy

“…Salinity stress [83] Bar Basta herbicide [84] EXPA3 Salinity tolerance [85] HKT, NHX1 and SOS1 Salinity stress [86] OVP1 Cold stress [87] PDR8 Non-host resistance [83] Pi-ta and Ptr(t) Blast [88] Rc, Bh4 and Phr1 Aging [31] Snl6…”