Effects of nitrogen levels on the expression of OsSWEET genes and the resistance to Xanthomonas oryzae pv. oryzae in bacterial blight susceptible and resistant rice cultivars

Abstract

Two prominent Thai rice varieties, namely Phitsanulok 2 (PSL2) and RD47, have historically been extensively cultivated in the lower northern region of Thailand. Unfortunately, their susceptibility to bacterial blight (BB) disease caused by Xanthomonas oryzae pv. oryzae (Xoo) has led to significant yield losses in this area. The spread and severity of BB disease are also influenced by farm management practices. This research aimed to investigate the impact of varying nitrogen fertilizer levels on both the severity of BB disease and the expression of the Sugars Will Eventually be Exported Transporters 11 (SWEET11) and SWEET14 genes in the rice cultivars RD47, PSL2, and IRBB21.

Rice plants were subjected to inoculation with Xoo isolate Xoo16PK002, which was obtained from the Phitsanulok province. A direct correlation between BB disease severity and increasing nitrogen concentrations, ranging from 16 kg/rai to 36 kg/rai, was observed. Fourteen days after infection (dai), the BB-resistant cultivar IRBB21 exhibited the highest resistance against Xoo16PK002, while the PSL2 and RD47 cultivars proved to be completely susceptible.

Differential expressions of SWEET11 and SWEET14 were detected in rice plants subjected to varying nitrogen levels during the early stages of plant development. Notably, the expression of SWEET11 displayed a substantial increase at 48 and 72 hours post-infection (hpi), while the expression of SWEET14 remained undetectable. These expression patterns suggest that Xoo16PK002 harbors the TAL effector PthXo1, which specifically targets the Effector Binding Elements (EBEs) of SWEET11 but not those of SWEET14, within the indica rice cultivars RD47, PSL2, and IRBB21.

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