1. 미국에서는 지난 10여년간 벼를 주식으로 소비하는 아시아계와 라틴 아메리카계 인구의 급격한 증가와 더불어 사회적 건강에 대한 관심의 증대로 인해 벼의 생산과 소비가 점차적으로 증가하고 있다. 2. 미국에서 생산되는 모든 벼의 99 퍼센트가 알칸소, 캘리포니아, 루이지애나, 미시시피, 미주리, 텍사스 등의 6개 주에서 생산되고 있으며, 주로 인디카 장립종을 재배하고 있는 다른 주에 비해 캘리포니아에서는 주로 자포니카 중립종과 단립종을 재배하고 있다. 3. 캘리포니아는 이상적인 기후와 충분한 농업용수의 공급 및 혁신적인 농업 기술의 이용으로 미국에서 가장 높은 9,000 kg/ha이상의 수량을 보이고 있으며, 레이저를 이용한 토지 평탄 시스템의 도입과 관수 시스템의 재순환을 통해 농업용수 이용효율을 지난 30년간 1/3 정도 향상시켰다. 4. 캘리포니아에 벼재배에서 사용되는 종자의 90% 이상은 종자의 순도유지 및 잡초 종자의 유입을 배제하기 위해 등록및 특화된 종자를 사용하고 있으며, 주요 파종 방법은 최아된 종자를 이용한 100% 담수직파에 의존하고 있다. 균형있는 비료의 시비를 위해 질소비료 및 다른 형태의 비료를 토양 및식물의 잎조직분석법의 의해 평가된 비료 요구도에 따라 기비및 추비의 형태로 살포한다. 5. 캘리포니아의 벼담수직파방법은 적미와 다른 잡초를 제어하는 효율적인 재배기술인 반면 담수 환경에서 발생하는 높은농업용수공급 비용, 벼유묘활착이나 초기 생육을 방해하는 수많은 무척추동물종의 출현, 새롭게 출현하는 제초제 저항성 수생잡초 등의 문제를 해결하는 것이 시급한 과제로 남아 있다.

In the facultative long-day (LD) plant Arabidopsis thaliana, FLAVIN-BINDING, KELCH REPEAT, F-BOX1 (FKF1) is activated by blue light and promotes flowering through the transcriptional and post-transcriptional regulation of CONSTANS under inductive LD conditions. By contrast, the facultative short day (SD) plant rice (Oryza sativa) flowers early under inductive SD and late under non-inductive LD conditions; the regulatory function of OsFKF1 remains elusive. Here we show that osfkf1 mutants flower late under SD, LD, and natural LD conditions. Transcriptional analysis revealed that OsFKF1 up-regulates expression of the floral activator Ehd2 and down-regulates expression of the floral repressor Ghd7; these regulators up- and down-regulate Ehd1 expression, respectively. Moreover, OsFKF1 can upregulate Ehd1 expression under blue light treatment, without affecting the expression of Ehd2 and Ghd7. In contrast to the LD-specific floral activator Arabidopsis FKF1, OsFKF1 likely acts as an autonomous floral activator because it promotes flowering independent of photoperiod, probably via its distinct roles in controlling expression of rice-specific genes including Ehd2, Ghd7, and Ehd1. Like Arabidopsis FKF1, which interacts with GI and CDF1, OsFKF1 also interacts with OsGI and OsCDF1 (also termed OsDOF12). Thus, we have identified similar and distinct roles of FKF1 in Arabidopsis and rice.

Heading date and photoperiod sensitivity are fundamental traits that determine rice adaptation to a wide range of geographic environments. By quantitative trait locus (QTL) mapping and candidate gene analysis using wholegenome re-sequencing, we found that Oryza sativa Pseudo-Response Regulator37 (OsPRR37; hereafter PRR37) is responsible for the Early heading7-2 (EH7-2)/Heading date2 (Hd2) QTL which was identified from a cross of late-heading rice ‘Milyang23 (M23)’ and early-heading rice ‘H143’. H143 contains a missense mutation of an invariantly conserved amino acid in the CCT (CONSTANS, CO-like, and TOC1) domain of PRR37 protein. In the world rice collection, different types of nonfunctional PRR37 alleles were found in many European and Asian rice cultivars. Notably, the japonica varieties harboring nonfunctional alleles of both Ghd7/Hd4 and PRR37/Hd2 flower extremely early under natural long-day conditions, and are adapted to the northernmost regions of rice cultivation, up to 53° N latitude. Genetic analysis revealed that the effects of PRR37 and Ghd7 alleles on heading date are additive, and PRR37 down-regulates Hd3a expression to suppress flowering under long-day conditions. Our results demonstrate that natural variations in PRR37/Hd2 and Ghd7/Hd4 have contributed to the expansion of rice cultivation to temperate and cooler regions

The timing of flowering, which is of crucial importance for plant growth and survival, is controlled by intricate pathways. To identify heading date-QTL, we constructed high resolution map on chromosome 3 using heterogeneous inbred family-near isogenic lines (H-NILs) derived from F7 RILs generated by the cross of early-heading japonica rice ‘H143’ and middle-late-heading indica-japonica hybrid cultivar ‘Milyang23’. QTL and subsequent sequence analysis using H-NILs revealed that the gene underlining QTL EH3, which is detected in the region of Hd16, is EL1 encoding casein kinase I (CKI). Two types of single amino acid substitutions in Ser/Thr kinase domain of EL1 were found in various cultivars, among which H-NIL(eh3) caused loss of function in EL1 demonstrated by altered heading date and GA response. Moreover, the phosphorylation of EL1 appears to involve in EL1 activity to regulate heading date. Transcriptional analysis clearly indicated that H-NIL(EH3) suppresses heading under LD conditions by down-regulating Ehd1, there by Hd3a and RFT1 expressions were not induced, suggesting that EL1 is photoperiod-sensitive and functions as a LD-specific suppressor of heading. Further characterization suggested that EL1 is likely to involve in anther development and seed settings by regulating GAMYB expression. Our study demonstrated that the genetic basis of natural variation occurred in ‘H143’ was revealed by QTL analysis using H-NILs, and EH3/EL1 function is crucial for heading and development in rice. The genetic natural variation of H-NIL(eh3) may have contributed to adaptation of rice cultivation to the higher regions by regulating the expression of rice flowering activator genes and GA signaling.